This key was created as a resource for those interested in learning to identify native trees in Wyoming. A page is provided for each tree species with photos and detailed descriptions about the plant species and the native range in Wyoming. The list of Wyoming Native Trees was derived from the PlantMaps.com - Native range maps have been cross-referenced and verified with multiple sources including https://www.fs.fed.us/database, commons.wikimedia.org, and various .edu entities.
The WY Native Tree ID Tool (online key) was modified and adapted from Identification Key for Woody Plants of the Pikes Peak Region by Colorado State University Extension, El Paso County. The original printed publication also contains a key for commonly planted landscape trees and includes conifers and deciduous shrubs. Additional information was sourced from the Colorado State University Forest Eco-geography course material, many identifying features listed were also compiled from Virginia Tech Dendrology Fact Sheets.
If you are interested in identifying ornamental trees, an online Key to Identifying Common Colorado Landscape Trees by Linda Smith, Christine Prins, and David Whiting. The online tool includes deciduous trees only.
Drawings and graphics were snipped from the original CSU Extension document and numerous online sources. Photos are credited to where they were sourced online, otherwise tree photos are property of Wyoming State Forestry Division. It is our hope to collect our own photo catalog and replace borrowed images over time.
Foliage
Scale-like, overlapping, hugging the branch?
Are the branches rounded or flattened?
Needle-like, long slender?
Are the needles growing singly along the stem, or
Are there two or more needles attached together at the base by a paper sheath?
Are the needles straight, curved, twisted?
Are they very thin or very thick?
Sharp or blunt at the tips?
Flexible or stiff? Can you bend them between your fingers when holding them at each tip, or do they break?
Color (may range from yellowing-green to bluish-green)
Length (this is where it's handy to have a small ruler with you out in the field) - length is variable, depending on the environment
Shape in cross-section (could be flat, round, or squared)
Is there an odor when the needle or scale is crushed or broken?
Are needles grooved along the mid-section, notched at the tip, or tapered at the base or tip?
Notice how the needles grow along the stem
Do they radiate completely around the stem?
Do they all grow forward toward the tip of the stem?
Do they grow along the upper half of the stem only, or along the sides?
Are there any white dots, resin or other gummy substances on the needles or scales?
Are there white "stripes" on either side of the needle?
Or a white "bloom" that can be easily rubbed off?
Bud
Size - depends on times of the year - buds expand into new growth from mid to late spring/early summer. The rest of the year, buds should be visible.
Shape (long, pointed, round, etc.)
Color (uniform throughout the bud, or are the scale margins a difference in color than the rest of the bud scale?)
Texture (smooth, hairy, rough, gummy)
Solitary or multiple?
Scales (do they peel back away from the bud, or do they lay close to the bud?)
Stem
When the needle is pulled off of the stem, does it leave a leaf scar on the stem?
What shape is the scar?
Is it flat, concave, or raised?
Is it round or oval?
When the needle is pulled off, does it leave a stalk or projection on the stem?
Color
Texture
Odor when bruised or broken
Are there any galls or other abnormal growths?
Cone
Texture (woody, papery, thick, thin)
Color (yellow, dark brown, green, reddish or purple)
Size (length, width)
Shape (round, long, narrow, oval)
Are the cones "berry-like”, as in the Junipers?
Cone scales - are they prickly at the tips of each scale, with a short, thin or thick sharp point?
Are there "appendages" (bracts) hanging over each scale, like a separate piece?
What is the location of the cone?
At the end of the stem or along the stem?
Upright or hanging?
If no cones are present on the ground are there upright "stalks" still on the branches? (White fir cones disintegrate while still on the tree, leaving a central upright thin stalk)
Habit/Form
Notice from a distance the general form of the tree.
Is it roundish, oval, flat-topped, or vase-shaped?
Is it pyramidal, pointed, or spire-like?
Does it have a single trunk, is it multi-stemmed, or is it thicket-forming?
Is the branching very formal and symmetrical, or loose and irregular?
Is there a definite central leader that continues all the way to the top, or does the plant branch off with several or many main branches?
Where is the plant located?
Was it planted on private property, or is it growing naturally?
Is it a cultivated, native, or naturalized tree?
Foliage
Leaf arrangement:
Are there two leaves that are directly opposite each other on the stem? (opposite)
Are the leaves arranged on the stem one at a time, alternating sides? (alternate)
Are the leaves almost opposite each other? (sub-opposite)
Are there three or more leaves attached to the stem at exactly the same point? (whorled)
Leaf type:
Is there just one leaf blade (and leafstalk) for each bud? (simple leaf)
Or is there more than one leaf blade (and leafstalk) for each bud? (compound)
Palmately compound (leaflets arranged so the leaflets radiate from one central point)
Pinnately compound (three or more leaflets arranged along a central stalk - one set of leaflets per bud)
Evenly pinnate (an even number of leaflets on the stalk - 6, 10, 12, etc.)
Oddly pinnate (an odd number of leaflets - 7, 15, 21, etc.)
Bipinnately compound more than one set of leaflets per bud - all leaflets arranged up and down a central stalk
Leaf margin (edge of leaf):
Are margin edges smooth or toothed (serrated)? If toothed, to what degree? (very fine and tiny to very large and coarse)
Are teeth pointed or rounded? Do they point toward the tip of the leaf or straight out?
Are there teeth within teeth (doubly serrated)?
Are margin edges wavy or lobed (indented)? Are the tips of the lobes pointed or rounded? If rounded, are there thin 'bristles' or hairs at the tip of each lobe? How many lobes?
Overall leaf shape:
Egg-shaped (ovate), oval, heart, round, diamond, triangular, narrow, oblong, lance-like?
Shape of leaf tip (apex):
A long, pointed tip, or a blunt, short tip? Rounded, straight across, heart shaped?
Shape of leaf base:
Rounded, heart-shaped, wedge-shaped, and straight-across? Or are the two sides of the base uneven, unequal, and lopsided?
Venation:
Which way do the veins run?
Are there several main veins originating from the same point at the base of the leaf? (palmate venation)
Or is there one central vein, with the side veins parallel to each other and straight, or irregular and curved? (pinnate venation)
Is there a very fine network of veins? (reticulate)
Do the secondary veins curve and run parallel to the margin and the main central vein, starting at the base and ending near the tip? (arcuate venation, sometimes called parallel)
Miscellaneous Leaf Features:
Stipules: tiny leaf-like appendages at the base of the petiole
Glands: very tiny bumps on top of the petiole, at the base of the leaf or on the leaf veins. It may be the same color as the leaf or a different color
Petiole: Leafstalk - is the stalk smooth or hairy? Notice the length. What is the general shape? Flat? Roundish? Is there milky sap that exudes from the stalk when pulled from the stem?
Leaf Color: could range from yellow/green to red/purple to blue/gray. Is the leaf the same color beneath as above?
Leaf Texture glossy, shiny, or dull? Is it thin or thick? Is it rough, sandpapery or smooth? Is it wrinkled looking? Is the texture the same beneath as above? Are there tiny hairs anywhere? Over entire surface, only at veins, or beneath?
Odor: When the leaf is crushed or torn, is there a distinctive odor?
Stem
Are there thorns, spines, or prickles? Large, thin, short, fat - what color are they, how thick are they? Are they very sharp, or not sharp at all?
Are there noticeable lenticels (dots on the stem - breathing pores). Raised or sunken; what color? Elongated horizontally or vertically?
Is the stem straight, or is it crooked or zig-zaggy? (Usually, the stems are zig-zaggy, also have a false terminal bud - the false terminal bud is not situated at the extreme tip of the stem. It is just a little to the side.)
What is the texture of the stem? Smooth, hairy, sticky, flaky, peeling?
Is there a white or blue “bloom” that you can rub off?
Size - is the stem thin, thick, ribbed, and grooved? Are there ridges? Is it round or square?
Color - of the outer bark and the inner bark.
Is there an odor to the stem when it is scraped, bruised or broken?
Notice if there are bits of bud scales still remaining at the terminal bud scale scars (the point on the stem that differentiates between last year’s growth and this year’s growth - several rows of scars encircling the stem - new growth will be tender and greenish, last year’s growth will probably be a little woody).
Are there spur shoots? (tiny, short stems that are very knobby with lots of horizontal ridges - they hold the flowers and fruit and are extra sturdy to hold that weight.) They are a good indication that the plant has fleshy, heavy, fruit instead of a dry fruit.
Is there a milky sap that exudes from a cut stem?
Bark on trunk - note the color and texture. Is it smooth, knobby, corky, peeling? Do the ridges run in a diamond shape, or vertically?
Bud
Buds are available for observation almost the entire year, except from bud break in the late spring to mid-summer. They develop in the axil of the petiole and the stem. In the winter, the bud is usually visible just above the leaf scar that is left on the stem after the petiole has fallen. A few plants produce a bud under the bark, within the base of the petiole; therefore the bud will be invisible in the summer, and will be in the center of the leaf scar in the winter.
Are buds whorled (more than two at one point around the stem)?
Are buds opposite each other on the stem, sub-opposite (almost opposite), or do they alternate along the stem (staggered)?
Do the side (lateral) buds stick out, away from the stem, or are they pressed closely to the stem?
Are they slightly stalked, or not stalked at all?
Are they lateral buds positioned in a vertical position, or are they slightly lopsided, tilting to one side or another?
Are they curved or twisted?
Is there only one bud at each node, or are there two or more (collateral or accessory) next to each other at each node?
Is there one bud directly above another at a node?
Is the terminal bud all alone, or are there several lateral buds positioned closely to the terminal bud, making a cluster of buds at the terminal?
Is the terminal bud a “true” terminal bud, or is it a “false” terminal bud? (A true terminal bud will be straight - a false terminal bud will be a little tilted to one side, and there may be a terminal branch scar near it, where the true terminal bud fell off, leaving a scar; sometimes this is very hard to determine.)
Also notice: Color - shape (pointed, round, etc.) - texture (sticky, smooth, hairy, leathery, shiny) - size.
Bud Scales
Do the scales overlap each other? (imbricate) There would be at least three scales in order to be imbricate.
Are there just 2 scales (rarely 3) that just barely meet and do not overlap? (valvate)
Some plants have only one bud scale (a single cap that fits over the bud and splits open when the bud expands in the spring)
Is the bud ‘naked,’ meaning that there are no hard scales, just a pair of developing leaves covering the bud?
Notice the arrangement of the scales around the bud. Are they:
Arranged on the bud in vertical rows of uniform ranks - one exactly above the other?
Arranged with the lowest scale centered directly over the leaf scar?
Arranged with the lowest scales paired at each side of the leaf scar?
Does the color of the individual scale change near the scale margin (at the top of each scale)?
Is there hair just on the scale margins, on the whole scale, or not at all?
What is the general shape of each scale? Is it long, short fat, narrow? Is there a vertical ridge in the center of the scale?
Are there remnants of old bud scales still attached at the base of the bud, from last year’s growth?
Leaf Scar
The leaf scar is the scar left behind on the stem when a leaf falls off at the end of the season. It’s the point at which the end of the petiole was attached to the stem. The scar assumes the same shape that the end of the petiole had - sometimes it’s hardly visible at all, and other times it’s quite large and distinctive. Each type of plant has its own special leaf scar and is a great help when identifying the different plants. During the growing season, there won’t be any leaf scars on the newest shoot growth - look at the leaf scar on last year’s shoot growth.
If the leaf scars are opposite each other on the stem, do they completely encircle the stem, with the ends of the scars meeting?
Is there a horizontal line connecting the two scars, or is there an open, clear area between the two scars?
What is the general shape of the scar? Narrow and thin, wide and fat, round, triangular, horseshoe-shaped? Curved or straight across?
Is the scar raised, sunken, or flush with the stem?
Does the bud sit on top of the scar, is it partially encircled by the scar, or is it totally enclosed inside the leaf scar?
Are there stipule scars (tiny, thin lines on each side of the leaf scar that indicate where the stipules were attached before they fell off)?
Whorled Alternate Opposite
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Leaf Types
Simple Compound
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Leaf Margins
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Leaf Shapes
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Venation
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Buds
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Bud Scales
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Leaf Scar
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Pith
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Habit
Vascular Bundle Scar/Traces
These are the scars (tiny dots) within the leaf scar that are formed when the leaf falls off and the vascular system (the xylem and phloem) between the stem and leaf is cut off.
Are the bundle scars visible at all?
Are they very distinct? How many are there?
Are there so many that they look like a blotch or a line? Are they raised, flush or sunken? (this is when a hand lens will come in very handy.)
Pith
The pith is the innermost portion of the stem. A penknife can be used to carefully scrape back a portion of the stem so that the pith can be seen. (Don’t do this on a large branch you don’t want to lose because it more likely will cause that particular branch to die.) The pith may be different in the current year’s growth versus last year’s growth. Check both.
Is the pith solid throughout, hollow throughout or just at the leaves or buds; spongy (large cavities); or is it chambered (hollow except for tiny partitions uniformly placed within the pith)?
What color is the pith - white, cream, brown, yellow, green, salmon?
Is it a relatively small pith, or does it consume a large portion of the stem in cross-section?
What shape is it in cross-section - round, star-shaped, oval?
Habit
Look at the plant overall - are there lots of small branches, or just a few main branches? During the growing season, is the plant so dense you can’t see through the leaves, or is it sparse, open?
What is the general branching pattern - upright, horizontal, pendulous?
Shape and form - round, oval, columnar, weeping, vase-shaped, cone-shaped, spire-like? Is it very formal and straight, or informal or irregular?
Is the plant multi-stemmed, thicket forming, or is it a single trunk?
Are there suckers at ground level?
Miscellaneous
Fruits and flowers may be on the plant for a very short time, but sometimes the stalk remains with remnants of dried fruit, which can provide a clue.
Is it a single stalk or a longer stalk with several side stalks coming off it?
Is the fruit fleshy or papery, dry or cone-like? Is it a furry, hairy, droopy catkin? If fleshy, how many seeds are inside?
Flower - note the color form, number of petals, time of bloom, fragrance. Does it bloom before, during, or after the leaves?
Check the ground near the plant for fallen fruit pods, or, in the winter, for fallen leaves. This is not a foolproof method of identifications, however, because the leaves or pods may have blown in from a neighboring plant.