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Really good definitions of many plant related terms are difficult to find. Many sources leave out details necessary to pin down the real meaning of words, fail to consider variations, add details that obscure proper meaning, or include misguiding or unclear statements. This document is an attempt to better define many of the words used when talking or writing about plants. Although every effort has been made to provide accurate and complete definitions and the definitions here are often superior to many from other sources, if highly technical or exact definitions are required, additional sourcing is advised.
- A -
Accession - the act of adding a plant to a collection.
Accession - a plant which was has been added to a collection. Also see taxon(taxa).
Accession record - a record kept for each plant in a collection that lists things like accession number, scientific name, provenance, date of acquisition, collection or purchase data, and physical location in the collection. Also see taxon(taxa).
Acclimate/acclimatize - to adapt to changes in climate or environment. Some of the climate and environmental factors, whose change may require a physiological response, include temperature, soil-moisture level, humidity, light exposure, wind exposure, and season. Also see harden-off and vernalization.
Acidic soil - soil having more hydrogen ions (H+) than hydroxide ions (OH-); having a pH level less than 7; "sour soil".
Adventitious bud - a bud that develops from somewhere besides apical meristem tissue (undifferentiated cell tissue, at the growing tips of roots and shoots, where most growth takes place). Adventitious buds may develop on stems, roots, or leaves. Their growth is often stimulated by wounds, pruning activity, or as a result of sudden exposure to higher light levels. Adventitious bud are especially important for root development on cuttings or layered stems and for development of tissue culture plants. Also see bud, callus, epicormic shoot, lateral bud, sucker, and watersprout.
Aeration - the process of adding air into the soil or growing media.
Air-layering - an above-ground method of propagation used to produce roots on an aerial stem while that stem is still attached to the parent plant. Many different schemes are used for air-layering, but often the stem is wounded, or partially cut, at the point where roots are desired and then wrapped in some sort of moist growing medium like sphagnum moss or potting soil inside a plastic wrap. Also see layering, marcot, and wounding (stem).
Alkaline soil - soil having more hydroxide ions (OH-) than hydrogen ions (H+); having a pH level more than 7; "sweet soil".
Allelopathy - stimulatory or inhibitory effects on biological organisms, caused by biochemical products from their neighbors or predecessors. Allelopathic effects can be beneficial (positive allelopathy) or detrimental (negative allelopathy). Allelopathic interactions between plants can occur with members of the same species or members of other species. Examples of plants known to produce allelochemicals include members of the Juglandaceae family, especially Juglans nigra (Black Walnut), which produce juglone; Ailanthus altissima (Tree of Heaven), which produces ailanthone; Centaurea maculosa (Spotted Knapweed), which produces catechin; members of the Brassicales order, especially Alliaria petiolata (Garlic Mustard), which produce glucosinolates; members of the Leucaena genus, such as Leucaena leucocephala (White Leadtree), and some members of the Mimosa genus, which produce mimosine; members of the Eucalyptus genus; various members of the Poaceae (true grasses) family, such as rice, wheat, and rye; etc. Also see allelochemical.
Allelochemical - a biochemical produced by one organism that causes a stimulatory or inhibitory effect in neighboring organisms or potential successors. Some types of allelochemicals are kolines (made by plants to affect other plants), phytoncides (made by plants to affect microorganisms), marasmins (made by microorganisms to affect plants), and antibiotics (made by microorganisms to affect other microorganisms). Also see allelopathy.
Androdioecious - having individuals that are all male and individuals with hermaphroditic flowers or sexual reproductive units (cones, etc). Also see andromonoecious, dioecious, gynodioecious, monoecious and trimonoecious.
Andromonoecious - having both male and monoclinous/hermaphroditic flowers or sexual reproductive units (cones, etc) on a single individual plant. Also see androdioecious, dioecious, gynomonoecious, and monoecious.
Angiosperm - a flowering plant. Angiosperms are seed plants whose ovules (undeveloped seeds) are enclosed by the ovary (a part of the female part of the flower). Angiosperms make up the Magnoliophyta phylum. Also see gymnosperm.
Anisophylly - having leaves of different shapes or sizes. Also see heterophyllous.
Annual - a plant whose life cycle in normally completed in one year; tender perennials are sometimes referred to as annuals if they are intended to be grown in an area where they are not hardy. Also see biennial, perennial, tender perennial.
Apical control - prevention or inhibition of growth of lateral branches by distal shoots, believed to be accomplished with the hormone auxin produced by the actively growing tips of the distal shoots. Also see apical dominance.
Apical dominance - prevention or inhibition of growth of branching lateral, or secondary, meristem by actively growing apical meristem, believed to be accomplished with the hormone auxin produced by the actively growing tip. Also see apical control.
Apomixis - ***** One of four types of asexual reproduction. Nonrecurrent apomixis occurs when meiosis takes place, but, instead of fusing with pollen, the female gamete forms a haploid embryo sac, from which the new plant forms. Nonrecurrent apomixis produces a haploid plant. Gametophytic apomixis occurs when meiosis is incomplete and an embryo is formed from only the female gametophyte. Plants formed from gametophytic apomixis are genetically identical to their parent. Adventitious apomixis occurs when meiosis is incomplete and an embryo is formed from ovule cells other than the female gametophyte. Adventitious apomixis produces plants that are genetically identical to the parent plant. Vegetative apomixis occurs when new plants are formed from plantlets or bulbils. Vegetative apomixis produces plants that are genetically identical to the parent plant.
Arboretum - a garden or parcel of land where trees and shrubs are collected and cultivated for educational, scientific, and/or aesthetic purposes. Also see botanical garden, orchard, and pinetum.
Arboriculture - the practice and study of cultivation of woody plants, especially trees.
Arborist - someone who specializes in the care and management of individual trees. Also see forester and silviculture.
Axillary Bud - a lateral bud, formed by apical meristem, at the junction of the stem and a leaf petiole and capable of developing into a shoot or flower. Also see adventitious bud, apical meristem, bud, epicormic shoot, lateral bud, nicking, notching, and terminal bud.
- B -
Balled-and-burlaped - a tree or shrub in the process of being transplanted whose rootball was dug up and wrapped for transportation or storage. The material used to enclose the rootball should be removed as much as possible without damaging the rootball when planted.
Bare root - a tree or shrub in the process of being transplanted whose roots have had all soil removed from around them. Bare roots must not be allowed to dry out excessively or damage to the roots or death of the plant may occur.
Bark - ***** Also see cork, cork cambium, lenticel, phloem, vascular cambium, and xylem
Bark inclusion - an area where the bark of a branch or trunk comes into direct contact with bark from another branch or trunk and is appressed so that cambium growth is prevented or reduced. Bark inclusion is commonly seen in the branch crotch of limbs with narrow crotch angles and between forks of codominant stems. Also see branch bark ridge, branch crotch, crotch angle, inosculate, and limb spreader.
Basal plate - An area along the bottom of a bulb or corm from which roots emerge and from which bulbets or cormlets are formed. Also see bulb and corm.
Berm - a raised mound of earth or other planting media with sloping sides used to add variety to a flat site, block noise, provide separation between different areas, provide more favorable planting conditions in areas with poor soil, hide undesirable views, create privacy, block access to restricted areas, direct drainage, provide a more protected area and better viewing opportunity for small or delicate plants, and/or provide other landscape functions.
Biennial - a plant whose life cycle typically spans two years. Also see annual, monocarpic, perennial, tender perennial.
Bigeneric hybrid - see intergeneric hybrid.
Bole - see trunk.
Bonsai - the Japanese art of miniaturizing trees or woody plants and developing them into aesthetically pleasing shapes by growing, pruning, and training them usually in specialized shallow containers. Also see hon non bo, niwaki, penjing, and saikei.
Botanical garden - a garden or parcel of land where a wide variety of plants are collected and cultivated for educational, scientific, and/or aesthetic purposes. Also see arboretum, orchard, and pinetum.
Branch bark ridge - A typically raised ridge of bark in a branch crotch where the branch and trunk tissue meet. When removing a branch, the final cut should be made just outside the branch bark ridge and the branch collar. Also see bark inclusion, branch collar, branch crotch, crotch angle, and limb spreader.
Branch collar - A sometimes bulging area of bark on the lower side of a branch at its base where the branch and trunk tissue meet. When removing a branch, the final cut should be made just outside the branch bark ridge and the branch collar. Also see branch bark ridge and branch crotch.
Branch crotch - the location at the union of a branch and trunk along the upper or terminal side, or, the location between two joining branches at the base of their union. Also see bark inclusion, branch bark ridge, branch collar, crotch angle, and limb spreader.
Broadleaf - having relatively broad as opposed to needle-like or scale-like leaves. Broadleaf plants can be deciduous, evergreen, or semi-evergreen.
Bud - a small lateral or terminal outgrowth on the stem of a vascular plant that may develop into a flower, leaf, or shoot and is often covered by protective scales. Also see adventitious bud, axillary bud, epicormic shoot, lateral bud / lateral shoot, nicking, notching, and terminal bud.
Bud union - the point at which a bud was grafted onto the rootstock or stem. Also see graft, graft union, rootstock, and scion.
Bulb - a modified underground stem with a bud or buds enclosed in fleshy modified leaves or scales, used to store food and moisture; a basal plate, ; and sometimes enclosed in a thin outer skin called the tunic. Daffodils, lilies, onions, and tulips are examples of bulb plants. Also see corm, geophyte, imbricate bulb, rhizome, tuber, tunic, and tunicate bulb.
Butt - the lower or basal portion of a tree trunk. Also see bole, crown, trunk, and root collar/crown/flare
- C -
Cabling - using cables and associated hardware to provide supplemental support and limit movement of leaders and/or individual branches. Also see dynamic cabling, rodding, and static cabling.
Caliper - a standard method of expressing the diameter, or thickness, of the trunk of a tree or shrub. The standards for measuring nursery stock are given by ANSI Z60.1-2004. It requires, "Caliper measurement of the trunk shall be taken six inches above the ground (for trunks) up to and including four-inch caliper size. If the caliper at six inches above the ground exceeds four inches, the caliper should be measured at 12 inches above the ground. Seldom are tree trunks perfectly round. The most accurate measurement will result from the use of a diameter tape. Caliper measurements taken with manual or electronic “slot” or “pincer” type caliper tools should be the average of the smallest and largest measurements." If the circumference of a trunk, at the proper height, is known, the caliper can be calculated by dividing that circumference by pi (approximately 3.14). Also see DBH.
Callus - undifferentiated plant tissue formed to cover a wound. Callus material can be used in micropropagation to grow genetically identical plants. Also see suberization and wounding (stem).
Cambium - See cork cambium, unifacial cambium, and vascular cambium.
Candle - ***** the new, soft shoot-growth of a conifer. Annual removal of a portion of each candle will result in a more full plant.
Canker - infected wound in plant cambium.
Central leader - ***** the trunk or a main stem, from which secondary stems (scaffold/secondary branches) originate. Also see bole and trunk.
Central leader pruning - ***** Also see modified central leader pruning and open center pruning.
Chalk - a typically light-colored, alkaline soil often containing large amounts of rock. Chalky soils dry out rapidly and tend to block nutrients like iron and magnesium so that they are unavailable to plants. Chalky soils can be heavily amended with organic material to make them more suitable for plants not well adapted to this type of soil.
Chill Hours - ***** Also see vernalization.
Chimera - a single plant or part of a plant composed of two or more genetically different types of cells. This phenomenon may be due to mutation of part of the original tissue or created by grafting.
Chlorophyll - one of at least six photosynthetic pigment biomolecules responsible for photosynthesis in all plants, most algae, and many species of bacteria. The three groups of photosynthetic pigments are chlorophylls, including Chlorophyll a (blue-green), Chlorophyll b (yellow-green), Chlorophyll c1, Chlorophyll c2, Chlorophyll d, and Chlorophyll f; carotenoids, including carotenes and xanthophylls; and phycobilins, including Phycoerythrobilin (red), Phycourobilin (orange), Phycoviolobilin/Phycobiliviolin (yellow absorbing), and Phycocyanobilin/Phycobiliverdin (blue). Also see photosynthesis.
Circadian response/rhythm - ***** Also see nastic movement and tropism.
Cladogram - a branching diagram that illustrates evolutionary relationships of groups of organisms. ***** Also see phylogeny and taxonomy.
Class - a primary taxonomic rank beneath the rank of phylum and above that of order. Also see taxonomy.
Clay - soil comprised mostly of particles less than 0.002 millimeters in diameter. Various standards define the upper limit of clay particle size between 0.001 and 0.004 millimeters. Clay soils usually retain moisture well and tend to be more nutrient-rich than other soil types. Potentially negative qualities of clay soils include poor drainage and aeration, tendency to easily compact, and being susceptible to frost heave. Also see loam, sand, and silt.
Cleaning (pruning) - removing dead, dying, diseased, low-vigor, rubbing, and structurally unsound branches. Also see pruning method.
Cleistogeal germination - a form of seed germination, found in the case of some tropical plants, in which a special umbrella-like leaf on a stalk forms above the ground and protects the plumule from damage. The cotyledons remain below the soil surface as in the case of hypogeal germination. The plumule emerges only after substantial development. Also see cotyledon, epigeal germination, germination, hypogeal germination, and plumule.
Climax Community - ***** Also see ecological succession.
Clone - ***** Also see genet, ortet, and ramet.
Clump - ***** a single plant with multiple trunks, or, a group of plants grown closely together so as to appear to be one plant. Also see standard.
Co-dominant stem/trunk - *****
Coir - the fibrous material and associated pith that makes up the thick mesocarp of coconut fruit. Also see coir peat.
Coir peat - a by-product of coconut husk fiber processing, consisting of the shorter fibers and residual dust (pith). Coir peat is sometimes used as a peat substitute for soil amendment or as a growing medium. It is often preferred to peat because of environmental reasons, its superior wetability, the fact that it degrades slower than peat, and its lower acidity. Unwashed coir may contain a large amount of salt which results from the retting process used to separate the fibers from the husk pith. Also see coir and peat.
Coleoptile - ***** Also see germination and hypogeal germination.
Collar - see branch collar. Also see branch bark ridge.
Columnar - having a narrow form. Columnar trees typically have a single trunk with short and uniform branch spread. Also see fastigiate.
Compaction (soil) - *****
Compartmentalization - forming barriers to the spread of decay by plugging the vertical vascular system of inactive xylem tissue, by developing concentric horizontal boundaries with summerwood cells of growth rings, by using radical walls created by ray cells, and by creating protective walls with vascular cambium when wounds occur.
Compost - *****
Conifer - ***** Deciduous conifers include members of the Glyptostrobus, Larix, Metasequoia, Pseudolarix, and Taxodium genera. Conifers and broad-leaved trees are not mutually exclusive; Members of the Agathis genus are examples of a broad-leaved conifers. Ginkgo biloba is not a type of conifer.
Coppicing - a pruning method where the trunk or trunks of a tree or shrub are cut at ground level or just above ground level to encourage regrowth. Coppicing can be used to regrow damaged trees, rejuvenate shrubs, or produce a rapidly-renewing source of wood. Periodic coppicing can keep a woody plant in its juvenile state and keep it from dying of old age. The base, or group of stumps, of a coppiced tree or shrub is referred to as a stool. Also see pollarding, pruning method, rejuvenation pruning, and stooling (pruning method).
Cork - ***** the outer most part of the bark. Also see bark, cork cambium, and phloem.
Cork cambium - ***** Also see cambium and cork.
Corm - a short thick solid underground stem, used to store food and moisture, with a basal plate, from which roots develop, and protective leaves modified into skins or tunics. Taro, Crocuses, Gladioluses, and Musas (bananas and plantains) are examples of plants with corms. Also see bulb, geophyte, rhizome, tuber.
Cotyledon - ***** Also see cleistogeal germination, epigeal germination, germination, hypogeal germination, and plumule.
Cross-species gene transfer - see lateral gene transfer.
Crotch angle - the angle, at the point of attachment, between a branch and the trunk or between two branches. Also see branch crotch and limb spreader.
Crown - the point at witch the trunk or trunks emerge from the root system. Planting the crown below grade or covering it with mulch can lead to rot, disease, and pest problems. Also see butt and root collar/crown/flare.
Crown (foliage) - ***** Also see apical dominance, decurrent branching habit, and excurrent branching habit.
Crown raising - removing branches from the bottom of a tree's crown to provide clearance, or, to improve timber quality and aid timber production. After pruning, the crown of landscape trees and younger timber trees should comprise at least two thirds of the height of the tree. Also see pruning method.
Crown reduction - reducing the height and/or spread of a tree's canopy by proper thinning and reduction cuts. Crown reduction can be used to reduce wind-load or weight for structural issues, allow for utility-line clearance, and to improve aesthetics. Even when done properly, crown reduction often results in large pruning wounds that may lead to decay and should be used only when necessary. Crown reduction is always preferable to topping, which employees heading cuts. Also see directional pruning, drop-crotching, pruning method, reduction cut, thinning cut, topping.
Crown restoration/renewal - selective pruning to improve the structure, form, and appearance of trees that have been damaged by improper pruning, physical damage, or disease. Also see pruning methods and topping.
Cultivar ("cultivated variety") - ***** a secondary taxonomic rank beneath genus and variety. Unique characteristics present in a cultivar may require asexual reproduction (vegetative reproduction). In some cases, cultivars may come true-to-type with sexual reproduction (seeds). Gleditsia triacanthos v. inermis 'Shademaster' or just Gleditsia triacanthos 'Shademaster' (here Shademaster is the cultivar name). Also see taxon(taxa) and taxonomy.
Cutting - ***** Also see half-mallet cutting / half-hammer cutting, hardwood cutting, heel cutting / torn cutting, lateral-shoot cutting, mallet cutting / hammer cutting, nodal cutting, semi-hardwood cutting, softwood cutting, terminal-shoot cutting, and truncheon.
Cyclic succession - ***** Also see Ecological succession.
Cyclophysis - ***** Also see topophysis.
- D -
DBH - diameter at breast height; a standard method of expressing the diameter, or caliper, of the trunk of a standing tree. The measurement can be directly measured, or, calculated from the circumference. Circumference divided by pi (approximately 3.14) gives diameter. For elliptically shaped trunks, the average of the larger and the smaller diameters can be used. The measurement is usually taken at 1.3 or 1.4 meters from ground level (for timber) or 1.5 meters from ground level (for large ornamental trees). On sloping ground, the reference point for ground level is usually the highest point on the ground touching the trunk, but sometimes the average between the highest and lowest points is used. If the point, at which DBH would normally be measured, falls on a swelling or bulge on the trunk, the measurement is usually taken below that area at the point where the diameter is the smallest. Also see caliper.
Deadhead - *****
Deciduous - a seasonal adaptation found in many plants from temperate zones where, sometime prior to winter, shoot growth ceases, resting buds are formed, and leaves are released from the plant. Some types of plants may be deciduous in colder climates but evergreen or semi-evergreen in warmer climates. Also see dormancy (plant), evergreen, and semi-evergreen.
Decurrent branching habit - ***** Also see apical dominance, crown (foliage), and excurrent branching habit.
Dendrochronology - the science of determining age of trees and evaluating past events, particularly climactic and environmental, by the analysis of tree rings. Also see growth ring.
Determinate - ***** a plant characteristic where growth substantially slows and fruit production is completed over a fairly short part of the growing season. Determinate tomatoes are often called bush tomatoes. Also see indeterminate.
Dicarpic - flowering and bearing fruit for two cycles during a lifetime. Some biennials are examples of dicarpic plants. Also see hepaxanthic, iteroparous, monocarpic, pleonanthic, plietesial, pollakanthic, polycarpic, semelparous, and tricarpic.
Dichogamy (Dichogamous)/Sequential Hermaphrodism - having male and female flower parts that mature at different times resulting in self-infertility and encouraging cross-pollination. Also see protandry, protogyny, and self-fertile.
Dicot/Dicotyledon - a flowering plant, or angiosperm, with a pair of leaves, or cotyledons, in the seed embryo. Dicots frequently have flower parts in groups of four or five; stem vascular bundles arranged in concentric circles; a well defined central root, developing from the seed radicle, from which secondary roots originate; pollen with three pores, or furrows; a network arrangement of major leaf veins; and unsheathed-base leaves with stalks (petioles) and stipules. Cactuses, lotuses, magnolias, and roses are examples of dicots. Also see eudicot and monocot.
Dimorphism - ***** a systematic variation resulting in two separate forms in individuals of the same species. Color, shape, size, and structure are examples of variable characteristics. Also see heteroblastic/heteroblasty, homoblastic/homoblasty, polymorphism, polyphenic trait, and sexual dimorphism.
Dioecious - having separate male and female individuals in a species of seed-bearing plants. Dioecious plants are not self-fertile. Also see androdioecious, andromonoecious, dichogamy, gynodioecious, gynomonoecious, monoecious, self-fertile, sexual dimorphism, and trimonoecious.
Diploid - having two complete sets of chromosomes, usually one set developed from each parent. Also see haploid, hexaploid, octaploid, ploidy, polyploid, tetraploid, and triploid.
Directional pruning - pruning in a manor that encourages growth in a desired direction or away from utility lines or other structures. Directional pruning reduces interference while minimizing harm to the tree and is a preferred alternative to topping. Also see drop-crotching and pruning method.
Domain - a primary taxonomic rank above the rank of kingdom. Also see taxonomy.
Dormancy (plant) - a period of halted or slowed growth. Many plants experience considerable root growth while their above ground growth halts or slows. Also see deciduous, herbaceous, and perennial.
Dormancy (seed) - a condition that prevents a viable seed from germinating. External, or exogenous, seed dormancy can be caused by physical (seed coating is impermeable to water), mechanical (seed coating is too hard to allow embryo expansion), or chemical (seed coating contains chemical germination inhibitors) factors involving the seed coating. Internal, or endogenous, seed dormancy can be caused by various morphological (embryo is not fully developed and needs additional growth after the seed is separated from the plant) or physiological (various embryo related factors may be involved) factors. Double dormant, or combinationally dormant, seeds are dormant for both external and internal reasons at the same time. Dormancy may be produced while the seed is still attached to the plant (primary dormancy) or generated after the seed is exposed to external conditions unfavorable to growth, like a dry environment (secondary dormancy). Factors required to overcome dormancy will vary with different types of seeds and with different conditions. These factors include such things as temperature, temperature fluctuations, exposure to light, passage of time, exposure to acids in the environment or in an animal's digestive tract, or physical penetration of the seed coat. Also see germination, orthodox seed, recalcitrant seed, scarification, stratification, and vernalization.
Drainable porosity - a quantity used in soil drainage equations equal to the ratio of the volume of water drained to the volume of the soil from which the water was drained. This quantity can also be expressed as the ratio of the depth of the water drained to the change in depth of the water table.
Drainage - ***** Also see field capacity, permanent wilting point, and soil interface.
Drip line - an imaginary line on the ground that corresponds to the outer edge of the leaf canopy. Some have erroneously proposed that this line also represents the extent of the root system of trees and shrubs.
Drop-crotching - a pruning method in which a limb is shortened back to a lateral branch that is at least one-third the diameter, at the point where the two meet, of the branch being pruned. Drop-crotching is often used for directional pruning and has definite advantage over topping, where heading cuts leave stubs. Disadvantages of this technique include large wounds which may not cover over quickly enough to prevent rot. Also see crown reduction, directional pruning, pruning method, and reduction cut.
Drupe - a fruit in which an outer fleshy covering (skin, or exocarp) surrounds a hardened shell (endocarp) which covers the seed. Fruits of the genus Prunus (almonds, apricots, cherries, nectarines, peaches, and plums), most palm fruits (coconuts, dates, and oil palm fruits), coffee beans, olives, mangoes, and dogwood fruits are examples of drupes.
Dwarf - a plant whose relative growth rate is slower and/or whose relative mature-size is smaller than a standard plant. Dwarf is defined by most conifer collectors as a conifer growing between 1" to 6" per year. After many years of growth, dwarf conifers can become very large. Also see miniature and dwarfing rootstock.
Dwarfing rootstock - ***** a rootstock used to limit growth rate and vigor, and often precociousness, of a plant. Dwarfing rootstocks vary in the degree to which they reduce growth rate. They may produce or contribute to a variety of characteristics including smaller plants, simpler and less frequent pruning requirements, reduced maintenance and management demands, and reduction of time until fruit production. Also see precociousness and semi-dwarf.
Dynamic cabling - ***** Also see cabling, rodding, and static cabling.
- E -
Early wood - see springwood
Ecological amplitude - *****
Ecological succession - ***** Also see climax community, cyclic succession, edge effect, invasive plant/species, monoculture, old-growth forest, pioneer community, primary succession, secondary succession, seral community/sere.
Edge effect - ***** Also see ecological succession, invasive plant/species, windsnap, and windthrow.
Epicormic shoot - a shoot formed from an adventitious or latent axillary bud, often as the result of wounding, pruning, or sudden exposure to higher light levels. Also see adventitious bud, bud, lateral bud, sucker, and watersprout.
Epigeal germination - a form of seed germination in which the seed, along with the cotyledon/cotyledons and plumule, is pushed above the soil surface. The first true leaves are produced at the tip of the growing shoot above the cotyledon/cotyledons. Also see cleistogeal germination, cotyledon, germination, hypogeal germination, and plumule.
Espalier - the horticultural technique of training woody plants by pruning, and possibly grafting, to create a single-plane, or two-dimensional, shape formed by the trunk and branches. Espaliered trees and shrubs are often trained on trellises, walls, fences, or wire supports.
Eudicot - ***** Also see dicot and monocot.
Evapotranspiration - a term used to represent the total water requirements for a plant. Evapotranspiration is the sum of the water lost through the leaves and stems of the plant, or transpiration, and the water lost through soil evaporation. Evapotranspiraton does not include run-off or water lost through drainage.
Evergreen - having foliage which persists and stays green throughout the entire year. Also see deciduous and semi-evergreen.
Excurrent branching habit - ***** Also see apical dominance, crown (foliage), and decurrent branching habit.
Extant - still in existence; not extinct. Also see extinct.
Extinct - no longer in existence; no longer living. Also see extant.
- F -
F1 hybrid - the first generation of seeds or plants that results from the cross pollination of two distinctly different parent plants or two distinctly different parent plant groups. The F1 generation may be intraspecific, interspecific, intergeneric, or interfamily. In the case of intraspecific F1 hybrids, the parents are often members of two "pure", or inbred, lines/strains. F1 hybrids are often much more vigorous than their parents, and this is referred to as heterosis or hybrid vigor. Also see F2 hybrid, heterosis/hybrid vigor, interfamily hybrid, intergeneric hybrid/bigeneric hybrid, interspecific hybrid, intraspecific hybrid, and P generation.
F2 hybrid - the generation of seeds or plants that results from the cross pollination of two members of the F1 generation. F2 hybrids may be referred to as second generation. Considerable genetic variation may be found in the F2 generation with various combinations of genetic traits, for each of the original parents, represented. F2 hybrid plants may not have the heterosis/hybrid vigor found in the F1 generation. Also see F1 hybrid, heterosis/hybrid vigor, and P generation.
Facultatively (as in facultatively deciduous) - exhibiting a characteristic under certain environmental conditions but not under others. A facultatively deciduous plant might be deciduous in the colder parts of its range, but evergreen in areas with warmer winters.
Family - a primary taxonomic rank beneath the rank of order and above that of genus. Also see taxonomy.
Fastigiate - having erect, parallel branches or trunks which produce a narrow form that tapers toward the top. Also see columnar.
Feathered - having branches. Also see whip.
Field capacity - ***** the amount of moisture in the soil after all gravitational water drainage has taken place. At field capacity, smaller soil pores are filled with water but larger pores are filled with both water and air. Also see drainage and permanent wilting point.
Field collection number - *****
First cover - A time usually defined as 10 days after petal fall in which a spray application is applied, usually to fruit trees. An application applied at petal fall is the petal fall application, the next application (first cover) is made after ten days, the following application (second cover) is made ten days after the first cover application, and it continues from there. Also see second cover.
Forest - ***** Also see Ecological succession and old-growth forest.
Forester - someone who specializes in the care and management of forests (large groups of trees). Foresters may be involved with forest-related conservation, timber harvesting, forest safety, and/or other aspects of forest management. Also see arborist and silviculture.
Forma (Form) - a secondary taxonomic rank beneath the rank of variety. Characteristic differences that define a forma are sporadic within a population, and offspring do not necessarily share the trait with their parents. Forma names are written as: Cornus florida f. rubra (here rubra is the forma name). Also see polymorphism and taxonomy.
Freezing-induced cell dehydration - the process where cellular moisture is reduced when water is frozen in areas between a plant's cells. Ice can form outside cell walls first because of the greater number of freezing nuclei present there and the phenomenon of supercooling. The lower vapor pressure of the intercellular ice draws moisture, with a higher vapor pressure, from inside the cells. Plants utilizing this method must be able to tolerate ice within intercellular spaces and withstand the stress of the resulting cellular dehydration. This process works in conjunction with freezing point depression of the cellular solution. Also see freezing point depression of cellular solutions and supercooling.
Freezing point depression of cellular solutions - reduction of the temperature at which cellular fluid freezes by the presence of certain solutes in the cellular fluid. When water content is reduced by freezing-induced cell dehydration, the higher solute concentration present inside the cells decrease the temperature at which freezing will occur. Also see freezing-induced cell dehydration.
Frill - ***** Also see girdle and ring.
Frost crack - ***** Also see Sun scald.
Frost heave - expansion and upward movement of soil caused by freezing and thawing. Frost heave can damage plant roots by breaking them and by exposing them to air causing rapid dehydration.
Fruit - the matured ovary, or ovaries, and, in some cases, associated parts, of a plant which may contain a seed or seeds. Many types of fruit categories have been identified, and many of these categories overlap or contain members whose characteristics make their classification uncertain or debatable. Also see drupe, nut, and pome.
- G -
Gall - ***** a localized abnormal growth resulting from parasitic organisms or insects.
Genet - ***** the group of offspring, or ramets, clonally reproduced from a single parent plant, or ortet. Also see clone, ortet, and ramet.
Genus (Genera) - a primary taxonomic rank beneath the rank of family and above that of species. Genus is the first component of an organism's binomial nomenclature, or scientific name, and should be written with the first letter capitalized. Example: Ginkgo biloba (here Ginkgo is the genus name). Also see taxonomy.
Geophyte - a herbaceous plant with an underground storage organ such as a bulb, corm, tuber, rhizome, tuberous root, or enlarged hypocotyl. Alliums, cannas, crocuses, daffodils, dahlias, potatoes, and tulips are examples of geophytes.
Germination - a process where the plant embryo within a seed, spore, or other reproductive body starts to grow, usually after a period of dormancy. Absorption of water, temperature, temperature fluctuations, exposure to acids in the environment or in animal's digestive tracts, and light exposure are some of the things that can influence or initiate germination. Also see cleistogeal germination, coleoptile, cotyledon, epigeal germination, hypogeal germination, and plumule.
Girdle - ***** Also see frill and ring.
Girdling root - a root that encircles part or all of the trunk of a tree or shrub, or other parts of the root system of such a plant, and therefore strangles the plant. Pressure on the trunk or root, caused by a girdling root, can cut off food and water movement and therefore seriously weaken or kill the tree or shrub. Girdling roots are often caused by potbound conditions or improper transplanting procedures.
Graft - A process where the tissue of one plant is caused to fuse together with that of another plant or, in some cases, where the tissue of one part of a plant is fused together with another part of that same plant. Grafting is a common way to propagate cultivars of many plants. Commonly, a scion is obtained from a desirable cultivar and grafted to a rootstock to produce a new plant with the characteristics of the plant donating the scion. Many commercially produced fruit trees such as apple and pear trees are produced by grafting a standard variety onto a seedling or standard rootstock. Also see bud union, graft union, inosculate, rootstock, and scion.
Graft union - the point at which a bud or scion was grafted onto the rootstock, branch, or trunk. Also see graft, graft union, rootstock, and scion.
Gravitational water drainage - movement of water through large soil pores influenced solely by gravity.
Grex (Greges) - ***** A hybrid cross between two orchid species, between an orchid species and another grex, or between two greges. The grex name includes the original cross and its reciprocal (a x b and b x a). Also see hybrid and nothospecies.
Groundcover - *****
Growth ring - the layer of wood (xylem) produced in one growing period. Also see dendrochronology, springwood, and summerwood.
Guttation - the discharge of xylem sap from hydathodes, rather than stomata, in plant leaves, that occurs in some types of plants when the osmotic root pressure exceeds transpirational pull.
Gymnosperm - seed plants whose ovules (undeveloped seeds) are exposed. Conifers, Ginkgos, Cycads, and Gnetae are gymnosperms. Also see angiosperms.
Gynodioecious - having individuals that are all female and individuals with hermaphroditic flowers or sexual reproductive units (cones, etc). Also see androdioecious, dioecious, gynomonoecious, and monoecious
Gynomonoecious - having both female and monoclinous/hermaphroditic flowers or sexual reproductive units (cones, etc) on a single individual plant. Also see andromonoecious, dioecious, gynodioecious, monoecious, and trimonoecious.
- H -
Half-hardy Perennial - see tender perennial.
Half-mallet cutting / Half-hammer cutting - ***** Also see cutting, hardwood cutting, heel (torn) cutting, mallet (hammer) cutting, nodal cutting, and truncheon.
Hammer cutting - see mallet cutting.
Hanger (1 of 2) - a lateral branch growing in a downward direction.
Hanger (2 of 2) - a detached branch lodged in a tree's canopy.
Haploid - ***** Also see diploid, hexaploid, octaploid, ploidy, polyploid, tetraploid, and triploid.
Harden-off - ***** Also see acclimate/acclimatize.
Hardiness zone - a geographic area or group of conditions usually applied to geographic areas where certain climactic conditions occur that determine what type of plant life can grow and survive. Frequently hardiness zones are determined by the average yearly minimum temperature which occurred during a specific sample time period, but other factors like the average number of days each year that a given region experiences high temperatures, ranges of temperatures in all seasons, precipitation, wind patterns, elevation, and length and structure of the growing season can also be used. Examples of hardiness zone schemes include the USDA Plant Hardiness Zones, The National Arborday Foundation Plant Hardiness Zones, American Horticultural Society Plant Heat Zones, Sunset (Magazine) Climate Zones, and Australian Plant Hardiness Zones.
Hardwood - wood from a dicotyledonous tree. Note that monocotyledonous trees do not produce wood and wood from a gymnosperm is referred to as softwood. The terms hardwood and softwood do not refer to the hardness of the wood. Hardwood has pores and a relatively complex structure. Softwood has no pores and is comprised mainly of simple longitudinal tracheids. Also see softwood.
Hardwood cutting - a cutting used to propagate a woody plant, that is taken from dormant, mature stems usually in late fall, after leaf drop, or during winter. Also see cutting, half-mallet (half-hammer) cutting, heel (torn) cutting, mallet (hammer) cutting, nodal cutting, semi-hardwood cutting, softwood cutting, and truncheon.
Head back / heading cut - to cut off the terminal portion of a branch or stem. Heading cuts can be used on some plants to create a fuller, more bushy plant. In other plants, especially many woody plants, heading cuts can be detrimental to the plant and cause wounds that the plant is unable to cover over before rot is initiated. Also see pollarding, pruning method, stub cut, tipping, and topping.
Heartwood - the central woody core of a woody plant derived from older sapwood. Heartwood is made up of non-living cells and provides support for the plant. Also see sapwood and xylem.
Heat zone - *****
Heel cutting / Torn cutting - ***** Also see cutting, half-mallet cutting / half-hammer cutting, hardwood cutting, mallet cutting / hammer cutting, nodal cutting, and truncheon.
Hepaxanthic - monocarpic. Considered an antonym of pollakanthic and pleonanthic. Also see monocarpic, pleonanthic, pollakanthic, and semelparous.
Herbaceous - type of plant whose stems die to the ground each year.
Herbarium - *****
Herbicide - a chemical used to kill unwanted plants.
Heteroblastic/Heteroblasty - the characteristic where leaves of the juvenile-stage of a plant and leaves of the adult-stage have significant differences in leaf size, shape, and/or growth habit. Also see dimorphism and homoblastic/homoblasty.
Heteroecious - *****
Heterophyllous - having leaves of different shapes or sizes. Also see anisophylly.
Heterosis / Hybrid Vigor - *****
Heterostyly - ***** Also see polymorphism.
Hexaploid - having six complete sets of chromosomes. Also see diploid, haploid, octaploid, ploidy, polyploid, tetraploid, and triploid.
Homoblastic/Homoblasty - the characteristic where leaves of the juvenile-stage of a plant and leaves of the adult-stage have only small differences in leaf size, shape, and/or growth habit. Also see dimorphism and heteroblastic/heteroblasty.
Hon non bo - the Vietnamese art of creating miniature mountainous, or mountainous island, landscape scenes, often set in water to represent the sea. Hon non bo works typically include large vertically-oriented rocks, representing mountains or islands, planted with miniaturized plants and trees. The scene is frequently built in shallow concrete bowls or trays, filled with water. Also see bonsai, niwaki, penjing, and saikei.
Horizontal gene transfer - see lateral gene transfer.
Horticulture - the practice and study of cultivation of plants for food and/or aesthetics.
Humus - fine-textured, decomposed organic matter.
Hybrid - ***** Also see grex, interfamily hybrid, intergeneric hybrid / bigeneric hybrid, interspecific hybrid, intraspecific hybrid, nothospecies, and ploidy.
Hypogeal germination - a form of seed germination in which the cotyledon/cotyledons remain below the soil surface and the coleoptile/plumule emerges above the soil surface, without the cotyledon/cotyledons, to produce the first true leaves. Also see cleistogeal germination, coleoptile, cotyledon, epigeal germination, germination, and plumule.
- I -
Imbricate bulb - a bulb without an outer paper-like protective covering, or tunic. Lilies are examples of imbricate bulb plants. Also see bulb, scaly bulb, and tunicate bulb.
Indeterminate - ***** a plant characteristic where growth continues and fruit production occurs over a relatively long portion of the growing season. Indeterminate tomatoes are sometimes called vining tomatoes. Also see determinate.
Index Seminum - ***** a list of seeds available for trade.
Inosculate - *****
Integrated Pest Management (IPM) - *****
Integrated Plant Management (IPM+) - *****
Interfamily hybrid - the product of a cross between members of different families from within the same order.
Intergeneric hybrid / bigeneric hybrid - the product of a cross between members of different genera from within the same family. The Leyland Cypress is thought to be an example of an intergenetic hybrid, but the taxonomy of one of its parents (the Nootka Cypress) is in question and could change this classification.
Interspecific hybrid - the product of a cross between different species within the same genus. Peppermint, a cross between Mentha aquatica (Watermint) and Mentha spicata (Spearmint), is and example of a interspecific hybrid.
Intraspecific hybrid - the product of a cross between two members from within the same species. A new cultivar formed from the cross of two other cultivars, or, the product of crossing two subspecies, would be examples of intraspecific hybrids. Crosses between plants with different ploidy are also examples of intraspecific hybridization.
Invasive growth (non-scientific) - aggressive growth or spread, to the point of being hard to control or contain.
Invasive plant/species - a non-native plant, introduced into an ecosystem, whose aggressive proliferation causes or has the potential to cause significant displacement or harm to native populations of plants or animals. Also see ecological succession, edge effect, and weed.
Iteroparous - polycarpic. Considered an antonym of Semelparous.
- J -
J-root - a root, usually a taproot, whose growth has been deflected to an upward direction. This phenomenon is often detrimental to the growth of the plant and is frequently caused by a potbound condition and/or poor transplanting practices.
- K -
Key - a flowchart used to identify a specific type (genus, species, cultivar, etc.) of plant.
Kingdom - a primary taxonomic rank beneath the rank of domain and above that of phylum. Also see taxonomy.
- L -
Lateral branch - a secondary branch originating from a scaffold branch or another lateral branch. Also see scaffold branch and secondary branch.
Lateral bud / lateral shoot - a bud / shoot formed along the side of a branch or stem. Also see adventitious bud, axillary bud, bud, nicking, notching, and terminal bud.
Lateral gene transfer - ***** Also see cross-species gene transfer and horizontal gene transfer.
Lateral-shoot cutting - ***** Also see cutting and terminal-shoot cutting.
Late wood - see summerwood
Layering - a method of plant propagation where an above-ground stem is buried in, wrapped in, or held against a growing media until roots are formed on the stem. Once a sufficient amount of root has formed, the stem can be removed from the parent plant to form a new plant. Also see air-layering and marcot.
Leader - a main shoot or stem from which lateral shoots or stems emerge.
Lenticel - ***** Also see bark.
Lignify (Lignification) - to become woody. Plant material is lignified by the formation of lignin in cell walls.
Limb spreader - *****
Liner - a young plant before it reaches the size typical of those sold at retail. Many retail nurseries buy liner plants and then allow them to grow larger before selling them. Also see feathered, sapling, seedling, and whip.
Loam - soil composed of relatively equal amount of clay, sand, and silt. Loamy soils combine good drainage, good tilth, and nutrient retention. Also see clay, sand, and silt.
- M -
Macroclimate - a regional zone of climate patterns and conditions. A macroclimate refers to an area larger than a mesoclimate and is customarily in the range of tens or hundreds of kilometers across. Factors that impact macroclimate conditions include such things as general topography and large geographic features (mountain ranges, large lakes or oceans, etc). Also see hardiness zone, mesoclimate, and microclimate.
Mallet cutting / Hammer cutting - ***** Also see cutting, half-mallet cutting / half-hammer cutting, hardwood cutting, heel cutting / torn cutting, nodal cutting, and truncheon.
Marcescence - *****
Marcot - (noun) the stem or branch used in air-layering. (verb) to air-layer.
Mature - ***** multiple meanings including: sexual maturity refers to a tree's ability to flower or to produce viable seed, given proper environmental conditions...or...mature size describes a tree's size (especially height) or canopy development when it reaches it's expected potential maximum size, in its current environment...or...refers to the desired size or age for a particular use...or...refers to production maturity, especially of a fruit-bearing plant. (physiological maturity). Also see rejuvenation.
Meiosis - *****
Meristem - undifferentiated cell tissue found in zones where growth can take place.
Mesoclimate - a local-area zone of climate patterns and conditions. A mesoclimate refers to an area larger than a microclimate and usually contains many microclimates. A mesoclimate is customarily in the range of tens of meters to a few kilometers across. An orchard, farm, valley, mountain, or city (ex. urban heat island) may be considered a mesoclimate. Mesoclimates can be influenced by many factors or combinations of factors such as large heat sinks or supplies (large paved areas, rocky areas, bodies of water, areas of vegetation), wind patterns caused by geography (mountains, large flat areas, etc), and variations in elevation (valleys, plateaus, mountains, etc). Also see hardiness zone, macroclimate, and microclimate.
Microclimate - a small zone where the climate differs from the larger, surrounding area. A microclimate can range in size from an area tucked into the crevice of a rock to an entire city. Microclimates can be produced by many factors or combinations of factors such as variation in sun exposure, heat sinks or supplies (rocks, pavement, walls, bodies of water, etc), localized wind patterns, and variations in elevation (depressions, valleys, hills, berms, roofs, etc). Also see hardiness zone, macroclimate, and mesoclimate.
Miniature - a plant whose relative growth rate is slower and/or whose relative mature-size is smaller than a dwarf plant. Miniature is defined by most conifer collectors as a conifer growing less than 1" per year. A dwarf grows between 1" to 6" per year, an intermediate grows between 6" to 12" per year, and a large grows more than 12" per year. Also see dwarf.
Modified central leader pruning - ***** Also see central leader pruning and open center pruning.
Monocarpic (Monocarp) - flowering and bearing fruit only once followed by death. Most agaves, most bamboos, most bromeliads, and many annuals and biennials are examples of monocarpic plants. Many annuals are not considered monocarpic because they flower and produce seed over a long period of time and continue to produce flowers even after initial fruit set. Also see annual, biennnial, dicarpic, hepaxanthic, iteroparous, pleonanthic, plietesial, pollakanthic, polycarpic, semelparous, and tricarpic.
Monoclinous - ***** Also see andromonoecious, dichogamy, dioecious, monoecious, synoecious, and trimonoecious.
Monocot / Monocotyledon - a flowering plant, or angiosperm, with a single leaf, or cotyledon, in the seed embryo. Monocots frequently have flower parts in groups of three; vascular bundles unorganized in stems; an aventitious (non-systematic) arrangement of roots; pollen with a single pore, or furrow; a parallel arrangement of major leaf veins; and leaves with a sheathed base and no stalk (petiole) or stipule. All bulb plants (daffodils, lilies, onions, tulips, etc), bananas, grasses (including bamboos and grains), orchids, and palms are examples of monocots. Also see dicot and eudicot.
Monoculture - *****
Monoecious - having male and female flowers or sexual reproductive units (cones, etc) on a single individual plant. Monoecious plants differ from monoclinous/hermaphroditic plants, which have bisexual flowers or sexual reproductive units, by having single-sex individual flowers or reproductive units. Monoecious plants may be self-fertile or non-self-fertile. Also see andromonoecious, dioecious, dichogamy, gynodioecious, gynomonoecious, monoclinous, synoecious, and trimonoecious.
Monopodial growth - ***** Also see orthotropic growth, plagiotropic growth, and sympodial growth.
Mulch - a protective covering placed over soil. Mulches can be organic (bark chips, shredded wood, pine needles, sawdust, grass clippings, hay, straw, leaves, paper, cardboard, compost, etc) or inorganic (rock, plastic sheeting, shredded rubber, old carpet, etc). Mulches can be used to improve soil fertility and texture as it breaks down, prevent germination of many weed seeds, reduce competition for food and water from grass and weeds, reduce erosion, help to maintain soil moisture during dry periods, aid drainage by preventing surface crusting and sealing, keep roots cooler during hot summer weather, help to moderate soil temperature fluctuations, reduce frost-heaving, reduce certain soil-borne diseases by preventing soil and fungi from splashing onto foliage, prevent damage from mowers and trimmers, and/or improve the look of the landscape. Also see weed.
- N -
Nastic movement - movement or growth of a plant, in response to an external stimulus, in a direction independent of that stimulus. Examples of types of nastic movement include chemonasty (in response to chemicals or nutrients), geonasty/gravinasty (in response to gravity), haptonasty/thigmonasty (in response to physical contact), hydronasty (in response to water), nyctinasty (in response to night-time conditions or darkness), photonasty (in response to light), seismonasty (in response to shock or vibration), and thermonasty (in response to temperature). Also see circadian response and tropism.
Native - a type of plant that evolved naturally in an area. Native plants are usually well adapted to climate and environment, beneficial to other native life forms found in the area, and stabilized in the area unless conditions are substantially changed.
Naturalize - to become well established in the wild in a region where not indigenous.
Nicking - ***** below the bud/branch to control shoot/branch vigor. Also see bud and notching.
Niwaki - the Japanese art of pruning trees so that their natural characteristics and form is enhanced, resulting in a living sculpture. Niwaki trees, although often kept smaller than typical full-size trees, are not miniaturized as are bonsai specimens, and are generally grown in the ground rather than in planters or pots. Cloud pruning is a common technique used in Niwaki. Also see bonsai, hon non bo, penjing, saikei, and topiary.
Nodal cutting - ***** Also see cutting, half-mallet cutting / half-hammer cutting, hardwood cutting, heel cutting / torn cutting, mallet cutting / hammer cutting, semi-hardwood cutting, softwood cutting, and truncheon.
Notching - ***** above the bud to encourage break (growth). Also see bud and nicking.
Nothospecies - ***** a hybrid species resulting from the cross between two species. A nothospecies contains the group of all offspring resulting from the original cross between the two parent species, all offspring resulting from crosses between members of the nothospecies, and all offspring resulting from backcrosses between members of the nothospecies and the original parent species. An example of a nothospecies is Magnolia x soulangeana, which is the result of crossing of Magnolia denudata and Magnolia liliiflora. Also see grex and hybrid.
Nut - *****
- O -
Octaploid - having eight complete sets of chromosomes. Also see diploid, haploid, hexaploid, ploidy, polyploid, tetraploid, and triploid.
Old-growth forest - ***** Also see climax community and ecological succession.
Open center pruning - *****
Orchard - a parcel of land where edible fruit and/or nuts are grown on trees, shrubs, and/or vines. Also see arboretum and botanical garden.
Order - a primary taxonomic rank beneath the rank of class and above that of family. Also see taxonomy.
Organic - *****
Ortet - ***** an individual plant from which clonal offsprings, or ramets, are vegetatively produced. Also see clone, genet, and ramet.
Orthodox seed - seeds that are tolerant of desiccation and have the ability to remain viable after being stored dry for extended periods of time (at least until the following growing season and, in some cases, for decades). All seeds can be classified as orthodox, recalcitrant, or intermediate, but these classifications are, in reality, part of a continuum. Also see dormancy (seed) and recalcitrant seed.
Orthotropic branching - ***** Also see plagiotropic branching.
Orthotropic growth - ***** Also see monopodial growth, plagiotropic growth, sympodial growth, and topophysis.
- P -
Parenchyma - ***** Includes ray cells and tracheids? Also see ray cell, tracheid, vessel element, and xylem.
Parthenocarpy (Parthenocarpic) - production of unfertilized or misfertilized fruit that is often seedless or contains only aborted or partially developed seed. Parthenocarpy may be produced by a stimulus such as pollination with incompatible or dead pollen, insect activity, or other stimulus (stimulative or aitionomic parthenocarpy), produced without stimulus (vegetative or autonomic parthenocarpy), or produced through the use of chemicals (artificial or chemical parthenocarpy). Vegetative parthenocarpy is believed to have developed as a mechanism for defense against predation. Seedlessness in seedless watermelons (produced by crossing a diploid parent with a tetraploid parent to produce triploid seed) is the result of stimulative parthenocarpy (in this case, caused by pollen incompatibility due to the ploidy of the hybrid plant). Some pear and fig varieties are examples of plants that can produce seedless fruit by vegetative parthenocarpy. Also see stenospermocarpy and seedless fruit.
Patent / Plant-patent - protection, granted by the federal government to the inventor or discoverer of an asexually-reproduced plant cultivar and lasting 20 years from the date of filing, prohibiting the asexual reproduction (for any reason) or selling of the plant cultivar without the permission of the patent holder. Also see plant variety protection, trademark / plant trademark, and utility patent / plant utility patent.
Pathogenicity - Ability of an infectious agent to result in disease or damage. Also see virulence.
Peat - a light, spongy, fibrous to mucky organic material found in temperate-zone wetlands and made up, primarily, of partially to mostly decomposed vegetation. Peat is sometimes used as a soil amendment to lower pH (acidify the soil), increase water-storage capacity, add nutrients, or change soil structure. Also see coir peat and sphagnum moss.
Penjing / Penzai - the ancient Chinese art of growing miniaturized trees and plants, typically as part of small-scaled representations of natural landscape, in pots and trays. Japanese bonsai was largely developed from penjing. Also see bonsai, hon non bo, niwaki, and saikei.
Percolate - to drain or pass through a porous material, as when water drains through soil or a growing medium.
Perennial - a plant that typically lives longer than two years. Although the term perennial is often used to refer specifically to perennial herbaceous plants, woody plants including trees, shrubs, and vines that live for more than two years are also perennials. Also see annual, biennial, polycarpic, tender perennial.
Permanent branch - *****
Permanent wilting point - ***** the amount of moisture left in the soil after much of the water, left at field capacity, has been evaporated into the atmosphere and plant roots have taken up all available remaining moisture. At the permanent wilting point the soil still contains moisture, but at levels insufficient for the plant roots to suck it out of the soil. If additional moisture is not supplied to the soil, plants will gradually die. Also see drainage and field capacity.
Petiole - a stalk, present on many plants, that attaches the leaf blade, or blades, to the stem.
P generation - ***** Also see F1 hybrid, F2 hybrid, interfamily hybrid, intergeneric hybrid/bigeneric hybrid, interspecific hybrid, and intraspecific hybrid.
Phloem - ***** living tissue of vascular plants that transports sap, or a water-based solution of sugars and other organic compounds produced by photosynthesis. Movement through phloem can be up or down and varies with season. In woody plants, the phloem is the inner most part of the bark and lies just outside the vascular cambium. Also see bark, vascular cambium, and xylem.
Photosynthesis - the process all plants, most algae, and many species of bacteria use to convert light energy into chemical energy (light dependent reaction) and store it, typically, in the bonds of sugar (dark reaction / Calvin cycle). In plants, photosynthetic algae, and certain types of photosynthetic bacteria, light energy, carbon dioxide, and water is converted into sugar and oxygen by chlorophyll in, except for the case of photosynthetic bacteria, chloroplasts. Anaerobic photosynthetic bacteria do not produce oxygen during photosynthesis and do not photosynthesize in the presence of oxygen. Most anaerobic photosynthetic bacteria use bacteriochlorophylls and other photosynthetic pigments, similar to the way higher plants use chlorophylls, to convert carbon dioxide and a substrate, such as hydrogen sulfide, into carbohydrates in a more primitive type of photosynthesis. Halobacteria, commonly found in environments where salt, moisture, and organic material are present, perform photosynthesis with bacteriorhodopsin and halorhodopsin, instead of chlorophyll. Archaea and some bacteria do not depend on photosynthesis for energy. Also see chlorophyll.
Phototropism - *****
Phylogeny - ***** Also see cladogram and taxonomy.
Phylum - a primary taxonomic rank beneath the rank of kingdom and above that of class. Also see taxonomy.
Phytosanitary certification - *****
Pinetum - a garden or parcel of land where conifers are collected and cultivated for educational, scientific, and/or aesthetic purposes. Also see arboretum and botanical garden.
Pioneer community - ***** Also see ecological succession.
Pith - *****
Plagiotropic branching - *****. Also see orthotropic branching.
Plagiotropic growth - ***** Also see monopodial growth, orthotropic growth, plagiotropic branching, sympodial growth, and topophysis.
Planting bar - ***** These are sometimes referred to as dibbles. Types of planting bars include the OST bar, the KBC bar, and the planting spear. Also see planting hoe.
Planting hoe - ***** Types of planting hoes include the hoedad or Rindt hoe, the plughoe, the Swedish planting hoe, and the Wifsta hoe. Also see planting bar.
Plant variety protection - protection, granted by the federal government (via the Plant Variety Protection Act / PVPA) to the breeder of a sexually-reproduced or tuber-propagated plant cultivar and generally lasting for 20 or 25 years from the date of certificate-issue, against sale, purchase, or transfer, without the permission of the cultivar's owner. Research exemptions and seed-saving provisions apply to PVPA cultivars as long as they are not prohibited by some other form of protection such as a utility patent. Similar protections, in other countries, are sometimes referred to as plant breeders rights. Also see patent / plant-patent, trademark / plant trademark, and utility patent / plant utility patent.
Pleaching - ***** Also see pruning method, pollarding, and topiary.
Pleonanthic - polycarpic. Considered an antonym of hepaxanthic. Synonym of pollakanthic. Also see hepaxanthic, pollakanthic, and polycarpic.
Plietesial - monocarpic but living for many years before flowering, bearing fruit, and dieing. Also see dicarpic, hepaxanthic, iteroparous, monocarpic, pleonanthic, pollakanthic, polycarpic, semelparous, and tricarpic.
Ploidy - ***** Also see diploid, haploid, hexaploid, octaploid, polyploid, tetraploid, and triploid.
Plumule - ***** Also see cleistogeal germination, cotyledon, epigeal germination, germination, and hypogeal germination.
Pollakanthic - polycarpic. Considered an antonym of hepaxanthic. Synonym of pleonanthic. Also see hepaxanthic, pleonanthic, and polycarpic.
Pollarding - a pruning method in which trees or shrubs are periodically headed back to maintain a shorter overall height and smaller, more dense crown (foliage) with vigorous regrowth and/or to produce a rapidly-renewing source of wood. Pollarding can keep a woody plant in its juvenile state and keep it from dying of old age. Pollard trees require consistent period maintenance and pruning. Also see coppicing, pleaching, pruning method, and stooling (pruning method).
Pollenizer - A plant, variety, or species that provides pollen. Also see dioecious, dichogamy, hybrid, monoecious, pollinator, and self-fertile.
Pollination - the transfer of pollen from the male plant parts that produce it to the female ovules or ovule-bearing organs. Pollination occurs in all seed-bearing plants. In the case of angiosperms, pollen is transfered from the anthers, the pollen-bearing part of the stamen (male flower part), to the stigma, the receptive end of the pistil (female flower part) which contains the ovules. Also see dichogamy, dioecious, monoecious, pollenizer, pollinator, and self-fertile.
Pollinator - An animal or other agent that successfully transfers pollen from the male organs of one flower to the female organs of another. Bees, bats, and birds are some of the more commonly recognized pollinators, but a variety of other insects and other types of animals also serve as pollinators. Wind is an example of a non-living pollinator. Also see pollenizer.
Polycarpic - flowering and bearing fruit multiple times during a lifetime. Most perennials and some annuals and biennials are polycarpic. Also see dicarpic, hepaxanthic, iteroparous, monocarpic, perennial, pleonanthic, plietesial, pollakanthic, semelparous, and tricarpic.
Polyembryony - ***** cleavage polyembryony, simple polyembryony, and adventitious polyembryony.
Polygamodioecious - mostly dioecious with a limited amount of perfect (bisexual) flowers present. Also see dioecious and trimonogamous.
Polygamous - *****
Polymorphism - ***** a systematic variation resulting in more than one form, in individuals of the same species. Color, shape, size, and structure are examples of variable characteristics. Also see dimorphism, forma, polyphenic trait, and sexual dimorphism.
Polyphenic trait - ***** Also see polymorphism.
Polyploid - ***** Also see diploid, haploid, hexaploid, octaploid, ploidy, tetraploid, and triploid.
Pome - a fruit with made up of several seed chambers and a pseudocarp. Examples of plants with pomes include apples, cotoneasters, loquats, medlars, pears, and quinces. Also see pseudocarp.
Pore Space - *****
Precociousness - ability to sexually mature and produce fruit at an early age. Also see dwarfing rootstock.
Primary succession - ***** Also see ecological succession, pioneer community, and secondary succession.
Protandry (Protandrous) - ***** Also see dichogamy and protogyny.
Protogyny (Protogynous) - ***** Also see dichogamy and protandry.
Provenance - ***** place of origin. Provenance can refer to geographic area, where a particular plant, seed, or variety was obtained, or, to a specific grower, breeder, or seller, particularly in the case of cultivated plants. Certain genetic traits may vary with provenance, particularly in cases where survival-of-the-fittest can result in a plant from one area being better adapted genetically for that area. In some cases, provenance may play a part in the creation of a species, subspecies, variety, or race.
Pruning method - ***** Also see central leader pruning, cleaning (pruning), coppicing, crown raising, crown reduction, crown restoration/renewal, directional pruning, head back / heading cut, modified central leader pruning, open center pruning, pleaching, pollarding, reduction cut, rejuvenation pruning, stooling (pruning method), stub cut, subordinating pruning, thinning cut, tipping, topiary, and topping.
Pseudocarp - the part of a fruit that does not originate from the ovary or ovaries. Examples of pseudocarps include the soft fleshy parts of apples, pineapples, or strawberries.
Pseudostem - ***** Also see bole, petiole, and trunk
Putative hybrid - *****
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- R -
Ramet - ***** a single member of a genet, or group of clonally reproduced offspring, vegetatively produced from a single plant, or ortet. Also see clone, genet, and ortet.
Random-access plant key - a program or system used to identify a type of plant, that allows the user to input only the available information.
Ray cell - ***** Also see parenchyma, tracheid, vessel element, and xylem.
Recalcitrant seed - seeds that are not tolerant of significant desiccation and do not remain viable after being stored dry for extended periods of time. All seeds can be classified as orthodox, recalcitrant, or intermediate, but these classifications are, in reality, part of a continuum. Also see dormancy (seed) and orthodox seed.
Reduction cut - pruning in which a limb is shortened back to a lateral branch that is at least one-third the diameter, at the point where the two meet, of the branch being pruned. Reduction cuts are often used for directional pruning and have definite advantage over heading cuts, used in topping, where stubs are left. Disadvantages of reduction cuts include large wounds which may not cover over quickly enough to prevent rot. Also see crown reduction, drop-crotching, and pruning method.
Rejuvenation - ***** Also see mature.
Rejuvenation Pruning - ***** Also see coppicing, pruning method, and stooling (pruning method).
Remontant - flowering more than once in a single season.
Rhizome - ***** an often underground, generally horizontal, main stem, typically with short internodes, often swollen and used to store food and moisture. Bamboo, bearded iris, Bermuda grass, ginger, Johnson grass, lily-of-the-valley, and water lilies are examples of plants with rhizomes. Also see bulb, corm, geophyte, root tuber, stem tuber, and stolon.
Ringing - removing a band of bark, or the outer portion, of a stem, branch, or trunk. Ringing can consist of exposing vascular cambium cells to aid in air-layering of a plant or can be used to sever phloem and vascular cambium layers to cause the death of a tree. Also see air-layering, girdle, marcot, phloem, vascular cambium, wounding (stem).
Riser - *****
Rodding/rod bracing - Also see cabling.
Root Collar/Crown/Flare - the area of interface between the trunk (or stem) and root system. Planting the root collar below grade or covering it with mulch can lead to rot, disease, and pest problems. Also see butt and crown.
Rootstock - ***** Also see bud union, dwarfing rootstock, graft, graft union, and scion.
Root tuber - a swollen root used to store food and moisture. Dahlias, sweet potatoes, and yams are examples of plants with root tubers. Also see bulb, corm, geophyte, rhizome, and stem tuber.
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Saikei - the Japanese art of creating miniature landscapes that contain miniaturized living trees, rocks, and sometimes associated plants and water features, usually in specialized shallow containers. Also see bonsai, hon non bo, niwaki, and penjing.
Sand - soil comprised mostly of particles between 0.05 and 2.0 millimeters in diameter. Various standards define the lower limit of sand particle size between 0.05 and 0.075 millimeters. Gravel is the standard classification of particle size above sand. Sandy soils have good drainage and aeration and are usually easily worked. Potential negative qualities include poor moisture retention and a lack of nutrients. Also see clay, loam, and silt.
Sapling - ***** Also see liner and seedling.
Sapwood - a relatively thin, newly-formed layer of wood (xylem) located between the heartwood and vascular cambium. Sapwood is made up of living and non-living cells and transports water, nitrogen, and mineral nutrients throughout a woody plant. Also see heartwood and xylem.
Saturation - point at which all available pore space is filled with water.
Scaffold branch - ***** Also see central leader and secondary branch.
Scaly bulb - see imbricate bulb.
Scarification - *****
Scion - ***** Also see bud union, graft, graft union, and rootstock.
Secondary branch - ***** Also see central leader, lateral branch, and scaffold branch.
Second cover - A time usually defined as 10 days after first cover in which a spray application is applied, usually to fruit trees. Also see first cover.
Secondary succession - ***** Also see ecological succession and primary succession.
Section - ***** a secondary taxonomic rank beneath the rank of genus and above that of series. Also see taxonomy.
Seedless fruit - a fruit without seed or with only partially developed seed. See parthenocarpy and stenospermocarpy.
Seedling - a young plant produced from a seed. Also see liner and sapling.
Self-fertile - ***** Also see dichogamy and dioecious.
Semelparous - monocarpic. Considered an antonym of Iteroparous. Also see hepaxanthic, iteroparous, and monocarpic.
Semi-dwarf - ***** Also see dwarfing rootstock.
Semi-evergreen - having foliage which persists and stays green throughout most of the year. Many types of plants may be evergreen in warmer climates but semi-evergreen in colder climates, or semi-evergreen in warmer climates but deciduous in colder climates. Also see deciduous and evergreen.
Semi-hardwood cutting - a cutting used to propagate a woody plant, that is taken from partially mature wood produced in the current growing season, just after a flush of growth. Also see cutting, hardwood cutting, nodal cutting, softwood cutting, and truncheon.
Senescence - *****
Seral community/Sere - ***** Also see ecological succession.
Series - ***** a secondary taxonomic rank beneath the rank of section and above that of species. Also see taxonomy.
Sexual dimorphism - ***** Also see dimorphism, dioecious, and polymorphism.
Sharp drainage - free passage of excess water and minimal water retention. Granite chips (poultry grit) or similar inorganic material is often added to soil to produce sharp drainage.
Shoot - *****
Silt - soil comprised mostly of particles between 0.002 and 0.05 millimeters in diameter. Various standards define the lower limit of silt particle size between 0.001 and 0.004 millimeters and the upper limit between 0.05 and 0.075 millimeters. Silt usually contains minerals (typically quartz) and fine organic particles and has a smooth/fine-grit texture (like flour) when dry. It is usually more nutrient rich than sand, holds water better than sand, and has better drainage than clay. Negatives may include poor drainage and surface crusting. Also see clay, loam, and sand.
Silviculture - the practice and study of raising forests. Also see arborist and forester.
Snag - a dead tree or shrub, still standing and available for use by wildlife. Snags provide shelter and food, in the form of insects, to many types of birds.
Softwood - wood from a gymnosperm. Note that wood from a dicotyledonous plant is referred to as hardwood and monocotyledonous plants do not produce wood. The terms hardwood and softwood do not refer to the hardness of the wood. Softwood has no pores and is comprised mainly of simple longitudinal tracheids. Hardwood has pores and a relatively complex structure. Also see hardwood.
Softwood cutting - a cutting used to propagate a woody plant, that is taken from soft, succulent, new growth just as it starts to harden/mature. Also see cutting, hardwood cutting, nodal cutting, semi-hardwood cutting, and truncheon.
Soil interface - ***** Also see drainage.
Soil types - usually an indication of particle size but may also be used to describe composition (peat, chalk, etc). Also see chalk, clay, loam, peat, sand, and silt.
sp. - an abbreviation used to represent the species part of a binomial nomenclature name when the actual specific name cannot or need not be specified. Also see spp.
Sphagnum moss - A large genus of mosses frequently found in peat bogs and often referred to as peat moss or bog moss. These terms, as well as moss peat, are also sometimes used to refer to dead, partially-decayed sphagnum moss when it becomes part of a decaying organic layer of peat. Sphagnum moss is sometimes used as a soil amendment, growing medium, or planting-container liner because of its ability to hold many times it's own weight in water. Also see peat.
Species - a primary taxonomic rank beneath the rank of genus. Species is the second component of an organism's binomial nomenclature, or scientific name, and should be written in lower case. Example: Ginkgo biloba (here biloba is the species name). Also see taxon(taxa) and taxonomy.
Sport - a part of a plant, or a plant propagated from such a part, with atypical morphological differences, typically as a result of mutation, from the rest of the plant. Many cultivars are derived from plant sports. Also see cultivar and witches' broom.
spp. - an abbreviation used to represent multiple species in a binomial nomenclature name when the actual specific names cannot or need not be specified. This abbreviation is the plural form of sp. Also see sp.
Springwood / Early-wood - lighter-weight wood characterized by larger cells with thinner cell walls and formed during the earlier part of the growing season. Springwood is usually the lighter colored part of the wood in a growth ring. Also see growth ring and summerwood.
Spur - *****
Standard - ***** a plant trained so as to have a tall single trunk, or, a tall single trunk onto which a plant, that often has a spreading or low-growing form, is grafted. Also see clump.
Static cabling - Also see cabling, dynamic cabling, and rodding.
Stem tuber - a swollen underground rhizome or stolon, without a basal plate or tunic, used to store food and moisture. Caladiums, potatoes, and tuberous begonias are examples of plants with stem-tubers. Also see bulb, corm, geophyte, rhizome, root tuber, and stolon.
Stenospermocarpy - production of a fertilized fruit that contains only aborted or partially developed seed. Seedless grapes are examples of stenospermocarpy fruit. Also see parthenocarpy and seedless fruit.
Strain - *****
Stolon - ***** a frequently at- or above-ground stem, typically with long internodes, originating from an axillary bud near the base of the plant and branching out to form new plant clones at the tip or at nodes. Mint, potatoes and strawberries are examples of plants with stolons. Also see rhizome and stem tuber.
Stooling (propagation method) - ***** Also see layering.
Stooling (pruning method) - see coppicing, pruning method, and rejuvenation pruning.
Stratification - ***** warm/cold seed treatment/storage. Also see vernalization.
Stub cut - ***** Also see head back / heading cut, pruning method, tipping, and topping.
Suberine - *****
Suberization - conversion of plant cell walls into corky tissue by infiltration of suberine. *****cacti & succulent*****
Subordinating pruning - *****
Subspecies - ***** Also see taxonomy and variety.
Sucker - ***** Also see epicormic shoot and watersprout.
Summerwood / Late-wood - more dense and less porous wood, with thick cell walls, formed during the later part of the growing season. Summerwood is usually the darker colored part of the wood in a growth ring. Also see growth ring and springwood.
Sun scald - ***** Also see frost crack.
Supercooling - a process where cellular liquid remains in a liquid state at temperatures below its normal freezing point because of the lack of a seed crystal or nucleus around which a crystal structure can form. "Deep supercooling" is believed to be instrumental in keeping plant cells from freezing down to, or below, temperatures of -20C. The supercooling process is also utilized to initiate freezing-induced cell dehydration by allowing water inside cells to remain liquid while intercellular water freezes. Also see freezing-induced cell dehydration.
Surfactant (wetting agent) - See wetting agent.
Sweating - ***** breaking dormancy. Also see dormancy (plant).
Sympodial growth - ***** include growth by substitution or apposition, zigzag. Also see monopodial growth, orthotropic growth, and plagiotropic growth.
Synoecious - ***** Also see andromonoecious, dichogamy, dioecious, monoclinous, monoecious, and trimonoecious.
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Tap root - a central root that develops from the seed radical and grows vertically downward from the stem. Taproots vary from a single central root to one of a few taproots and from long conical-shaped tapered roots to swollen tubers. Secondary roots grow laterally from the taproot. Taproots firmly anchor a plant and sometimes serve as a storage organs. Many plants originally grow a taproot as seedlings but then gradually develop a more wide-spreading fibrous root system with a more horizontal nature as they mature.
Taxon (Taxa) - ***** Also see accession and accession record.
Taxonomy - ***** Also see cladogram, class, domain, family, forma, genus, kingdom, order, phylogeny, phylum, section, series, species, subspecies, taxon(taxa), tribe, and variety.
Temporary branch - *****
Tender perennial - a plant frequently grown as an annual in colder areas but whose life cycle could span several years in warmer areas. Also see annual, biennial, half-hardy perennial, perennial.
Terminal bud - ***** Also see adventitious bud, axillary bud, and lateral bud.
Terminal-shoot cutting - ***** Also see cutting and lateral-shoot cutting.
Tetraploid - having four complete sets of chromosomes. Also see diploid, haploid, hexaploid, octaploid, ploidy, polyploid, and triploid.
Thinning cut - ***** Also see pruning method.
Thinning (pruning) - the selective removal of branches or stems to increase light penetration and air movement through the crown of a tree or the foliage of a plant. Thinning can reduce wind-load effects, reduce weight on heavy limbs, discourage disease, improve aesthetics, allow more sunlight to reach the ground, and stimulate flowering and fruit production. Cleaning should be done prior to, or as a part of, thinning. Also see cleaning (pruning), pruning method, and thinning cut.
Tilth - *****
Tipping - ***** lateral branches. Also see head back / heading cut, pruning method, stub cut, and topping.
Topiary - ***** Also see niwaki and pleaching.
Topophysis - ***** Characteristic of cuttings, scions, or buddings, taken from vertically-growing locations, where new growth maintain a branch-like, or plagiotropic-growth, habit for a period of time. Also see cyclophysis, orthotropic growth, and plagiotropic growth.
Topping (pruning) - ***** upright branches. Also see crown reduction, crown restoration/renewal, directional pruning, head back / heading cut, pruning method, stub cut, and tipping.
Torn cutting - see heel cutting.
Tracheid - elongated xylem cell of vascular plants that transports water, nitrogen, and mineral nutrients in horizontal directions. Tracheid cells also serve structural support and water and nutrient storage functions. Also see parenchyma, ray cell, vessel element, and xylem.
Trademark / Plant trademark - ***** Also see patent / plant-patent, plant variety protection, and utility patent / plant utility patent.
Translocate - *****
Transplant - *****
Transplant shock - *****
Tree - ***** This term can be used to describe certain plants included in the Pteridophyta division of tracheophytes such as members of the Cyatheales (Tree Fern) order, the Cycadales (Cycad) division of gymosperm spermatophytes, the Ginkgophyta (Ginkgo) division of gymosperm spermatophytes, the Pinophyta (Conifer) division of gymosperm spermatophytes, the primitive dicots clade in the Magnoliophyta (Angiosperm) division of spermatophytes, the monocot clade in the Magnoliophyta (Angiosperm) division of spermatophytes, and the eudicot clade in the Magnoliophyta (Angiosperm) division of spermatophytes. Examples in the monocot clade include some members of the Arecaceae (Palm) family, the Pandanus (Screw Pine) genus, and the Dracaena (Dragon Tree), Cordyline , and Yucca genera of the Asparagaceae family.
Tribe - a secondary taxonomic rank beneath the rank of family and above that of genus. Also see taxonomy.
Tricarpic - flowering and bearing fruit for three cycles during a lifetime. Also see dicarpic, hepaxanthic, iteroparous, monocarpic, pleonanthic, plietesial, pollakanthic, polycarpic, semelparous, and tricarpic.
Trimonoecious - *****
Triploid - having three complete sets of chromosomes. Also see diploid, haploid, hexaploid, octaploid, ploidy, polyploid, and tetraploid.
Tropism - movement or growth of a plant, in response to an external stimulus, in a direction determined by that stimulus. Examples of types of tropism include chemotropism (in response to chemicals), electrotropism/galvanotropism (in response to an electric field), geotropism/gravitropism (in response to gravity), heliotropism/paraheliotropism (in response to sunlight), hydrotropism (in response to water), photoperiodism (in response to seasonal or artificial light pattern changes), phototropism (in response to lights or color of light), rheotropism (in response to the flow of water), thermotropism (in response to temperature), thigmotropism (in response to physical contact), and traumatropism (in response to wounding). Tropism can result in growth or movement towards or away from the stimulus (orthotropism), at right angles to the stimulus (diatropism), or at various angles to the stimulus (plagiotropism). Also see circadian response and nastic movement.
Truncheon - ***** Also see cutting and hardwood cutting.
Tuber - see stem tuber or root tuber. Also see bulb, corm, rhizome.
Tunic - an outer paper-like membrane that covers and protects the fleshy modified leaves, or scales, of some bulbs. Also see bulb, imbircate bulb, and tunicate bulb.
Tunicate bulb - a bulb with an outer paper-like protective covering called a tunic. Daffodils, hyacinths, onions, and tulips are examples of tunicate bulb plants. Also see bulb, imbricate bulb, and tunic.
Trunk - ***** Also see bole and pseudostem.
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Understory - tendency to grow beneath the forest canopy. Smaller, shade-tolerant trees and shrubs, that tend to be found growing in the shade of larger trees, are described as understory trees. Also see groundcover.
Utility patent / Plant utility patent - *****protection for any plant type or plant parts, 20 years, reproducing or selling, possible to protect a class or group of cultivars with a specific trait, part, or method of reproducing, must not be found in nature.***** Also see patent / plant patent, plant variety protection, and trademark / plant trademark.
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Variegated (Variegation) - ***** chimera (Hosta), air pockets / blisters, pattern genes (Maranta, Actinidia kolomikta, Silybum marianum), transposons (Rosa galliea 'Versicolor', Pisum sativum, Zea mays "Indian Corn"), virus (Vinca major 'Reticulata', Viola odorata, Abutilon) ???
Variety - a secondary taxonomic rank beneath the rank of genus and above that of forma. Characteristic differences that define a variety are inheritable, and seedling offspring are produced true-to-type. Varietal names are written as: Gleditsia triacanthos v. inermis or Gleditsia triacanthos var. inermis (here inermis is the varietal name). Also see subspecies and taxonomy.
Vascular cambium - a layer of actively dividing cells between xylem (wood) and phloem (inner bark) tissues that results in the thickening of stems and roots. Also see bark, cork cambium, phloem, unifacial cambium, and xylem.
Vernalization - exposure to prolonged periods of cold temperatures, often measured in chill hours, that enables a plant to flower or develop further. Also see acclimate/acclimatize, chill hours, and stratification.
Vessel element - ***** absent in most gymnosperms. Also see parenchyma, ray cell, tracheid, and xylem.
Virulence - Ability of an infectious agent to spread within a host or between individuals. Also see pathogenicity.
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Watersprout - ***** Also see epicormic shoot and sucker
Weed - a plant growing in an undesirable place. A weed may be further described as invasive or non-invasive, aggressive or non-aggressive, and native or non-native. Also see groundcover, invasive plant/species, mulch, and native.
Wetting agent - surfactants that reduce the surface tension of water or another liquid, allowing it to more easily adhere to plant tissue or penetrate and wet the soil. Also see surfactant.
Whip - a young unbranched tree or plant. Also see feathered.
Windsnap - the breaking of the stem or trunk of a plant, especially a tree, by the wind. Also see edge effect and windthrow.
Windthrow - the uprooting and felling of a plant, especially a tree, by the wind. Also see edge effect and windsnap.
Witches' broom - mutations consisting of tightly congested formations of twigs and foliage. Many dwarf cultivars, especially dwarf conifers, are derived from cuttings taken from witches' brooms and propagated, frequently by grafting, as new varieties of the parent plants. The cause of some witches' brooms is not completely understood, but some of the things that are believed to play a part in initiating them include fungi, insects, mites, nematodes, parasites, phytoplasmas, and viruses. Many witches' brooms are the result of disease and not viable, while others are quite stable and make wonderful small versions of normally larger plants. Also see cultivar and sport.
Wounding (stem) - ***** using one or more method to expose more growth cells from the cambium layer, to aid in callus and adventitious root production, and/or to expose more xylem cells, to aid in water and nutrient uptake. Wounding can be accomplished by making longitudinal incisions into the base of a cutting, removing portions of outer bark along the base of a cutting, or crushing the basal end of a cutting. Wounding can also consist of making a cut partially through a stem, or ringing a stem, intended for layering or air-layering. Also see adventitious bud, air-layering, callus, marcot, and ringing.
- X -
Xeriscape - A method or style of landscaping and gardening that attempts to minimize the need for water and eliminate or greatly reduce the use of supplemental irrigation.
Xylem - The primary supporting tissue and principal conductor of water, nitrogen, and mineral nutrients in vascular plants. Movement through xylem is unidirectional (from roots up to other parts of the plant). The sapwood and heartwood of tree trunks, branches, and roots are made of xylem. Also see bark, cambium, heartwood, phloem, ray cell, sapwood, tracheid, vascular cambium, and vessel element.
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- Z -