Plant classifications

Fact: Today's oldest tree has a root system of 9550-years-old. 

Alternation of generations

Plant life cycles are different from animals, called the "alternation of generations", which has diploid and haploid states/generations. 

Note: "n" = number of chromosome sets

• diploid (2n): Cells with 2 full chromosome sets, one from each parent. Human diploid cells have 46 chromosomes (23 pairs). Most somatic (body) cells are diploid.

  • etm: Gr: "di-" from "dis" two/double + "ploid" from "ploïdēs" fold/form (relates to number chromosome sets)

• haploid (n): Cells with 1 full chromosome set. Humans haploid cells have 23 chromosomes, which includes gametes (sperm and egg cells), produced in meiosis.

  • etm: Gr: "haplo-" from "haploïdos" single/simple + ploid (same as diploid's)

Diploid phases make spores and haploid phases make gametes.

Most animal cells are diploid and undergo meiosis, making haploid sex cells, or gametes. 

2 haploid cells fuse in fertilization create a diploid zygote that grows into an animal (Figure 5(a)). 

Early adaptation on land

Most plant species today live on land and the primitive ancestors today's plants livein water and were probably like algae - relatively small.

Bryophyte

11B - Pg 86

Bryophytes are the simplest land plants, (mosses, liverworts, and hornworts). 

North America has 1000+ moss species. Peat mosses, of the genus Sphagnum, may be the most widespread plants globally. 

Many ecosystems have Sphagnum mosses forming a continuous ground cover over hundreds and thousands of square kilometres (Figure 7). 

Like early land plants, bryophytes have protective cuticles and stomata for gas exchange and no specialized vascular tissue or true leaves, roots, or seeds. Most are only a few centimetres in height.

• cuticle: waterproof, hard coat made by most plants' epidermis

  • etm: middle Fr: became La: "cutis", both skin

• stoma (pl. stomata): small openings in epidermis that do gas exchange

  • etm: Gr: "stoma" from "στόμα" mouth

Gametophyte generations of bryophytes create swimming sperm in antheridia structures (sing. antheridium) and eggs in archegonia structures (sing. archegonium). 

• antheridia: Saclike male reproductive organ in fungi, mosses, ferns, and other nonflowering plants.

  •  etm: Gr: “anter” from "ἀνθηρός" flower/pollen + “-idia” small

• archegonia: Female reproductive organ in ferns and mosses.

  • etm: Gr: “arche” from αρχή start + “gonia” from "γόνοζ" offspring

Lycophytes and Pterophytes

The next land plant adaptation is the development of vascular tissue, consisting of xylem and phloem, specialized in water and nutrient transportation. Plants with such tissue grow to great heights, gaining more sunlight. Lignin is a key chemical component of vascular tissue. It's a highly strong compound reinforcing cell walls, responsible woody tissues' great strength. 

The lycophytes (club mosses) and pterophytes (ferns and their relatives) are groups of seedless vascular plants that still have many characteristics of the earliest vascular plants. In the Carboniferous period, 360-300 million years ago, these plants dominated the landscape. Today’s 13k species are common, most being small. 

Among the simplest of vascular plants are called horsetails, considered as “living fossils” as the only remaining genus of what was once a diverse plant group. As they grow, silica crystals form on their stems.

Gymnosperms and Angiosperms: Seed Plants

Today most lycophytes and pterophytes grow in shadows of seed plants. 

Most of the male gametophytes are carried from one plant to another by wind or by animals, rather than travelling in water. Seed plants are thus not restricted to reproduction over short length in wet places, and became the dominant land plants on Earth.

Pollen grains are waterproof capsules conmicroscopic haploid male gametophytes (Figure 10(a)). Pollination occurs when male gametes in pollen grains penetrate ovules with a female gametophyte. The male gamete fertilizes an egg, creating a diploid zygote. This diploid zygote, or embryo, becomes a seed, with a food supply for the embryo inside a seed coat (Figure 10(b)). They vary in size from the gigantic seeds of the Coco de Mar, or sea coconut, with a mass of 17 kg+, to the microscopic seeds of some orchids, with a mass of less than 0.001 g! Seeds can remain dormant, for the embryo to sustain longer until conditions are suitable to germinate.

Nothern Ontario boreal forests are dominated by spruce trees, major source of lumber and pulp and paper, supporting many big ecosystems, home to many species. Some gymnosperms live for centuries and are the foundation of well-established and complex ecosystems. For instance, the Three Sisters (Figure 12) live in Carmanah Walbran Provincial Park in Vancouver. They're 3 Sitka 80 m tall spruces sharing an ancient root system of an ecosystem that are threats to the boreal forest.

Angiosperms: The Flowering Plants

90%+ of modern plant species are angiosperms or flowering plants. The more than 260 000 species of angiosperms dominate the modern world of plants. Except coniferous trees, mosses, and ferns, virtually all familiar trees, shrubs, and herbaceous plants are angiosperms. As their common name suggests, angiosperms have specialized reproductive structures called flowers. Flowers perform the same function as cones in producing both pollen and eggs. But, in female flower parts, eggs are protected in an enclosed ovary. After fertilization, seeds form within the ovary and the outer tissues of the ovary become a fruit. The main function of the fruit is to help disperse the seeds. Flower and fruit development are key to angiosperms' success. There are seed types in angiosperms, each with either one (“mono”) or two (“di”) cotyledons, are structures storing food for growing embryos during germination.

The 2 biggest flowering plant groups are the monocots and the eudicots. The monocots, having some 60k species, include more than 10,000 species of grasses and 20,000 species of orchids. Almost all flowering trees are eudicots. There are smaller groups that aren't part of either eudicots or monocots, like magnolias, cinnamon, black pepper, and water lilies (Figure 13). Flowers are very diverse (Figure 14(a) to (d)). These structures are specialized for the way the plant is pollinated. Many flowering plants are wind-pollinated. Th e fl owers on such plants are typically small and drab looking. Examples include the fl owers of grasses. Other fl owers are pollinated by animals such as bees, bats, and hummingbirds. These are often colourful and fragrant and produce nectar.