Tree Identification and Selection Practice Questions

Correct answer: B. The bristle-tipped oak is in the red oak group, so it needs attention first

Bristle tips on the leaf lobes mark the red oak group, which includes northern red, northern pin and black oaks. A red oak that shows oak wilt symptoms usually loses most of its leaves and dies within about a month, while white oaks decline much more slowly and may survive infection. Swapping the two groups would send protective effort to the less vulnerable tree.

• A: Rounded lobes without bristle tips are typical of the white oak group, not the red oak group.
• C: Only the rounded-lobed tree fits the white oak group; the bristle-tipped tree is a red oak and is highly susceptible.
• D: Bristle-tipped versus rounded lobes is a standard way to separate red oaks from white oaks, and the groups differ sharply in oak wilt susceptibility.

Sources: Oak Wilt, Wisconsin Department of Natural Resources ; Virginia Tech Dendrology Fact Sheet: northern red oak (Quercus rubra), Virginia Tech Department of Forest Resources and Environmental Conservation ; Virginia Tech Dendrology Fact Sheet: white oak (Quercus alba), Virginia Tech Department of Forest Resources and Environmental Conservation

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Correct answer: C. Quercus rubra: genus capitalized, epithet lowercase, both in italics

A scientific name is a binomial made of the genus followed by the specific epithet. The genus is capitalized, the epithet is written in lowercase, and the whole name is italicized (or underlined when italics are not available). Capitalizing the epithet is a common error, and writing the name in plain type or all capitals breaks the convention.

• A: The specific epithet is always lowercase.
• B: The genus must be capitalized, and the name should be italicized or underlined.
• D: Only the first letter of the genus is capitalized, and the whole name should be italicized or underlined.

Sources: Extension Gardener Handbook, Chapter 3: Botany, NC State Extension ; Extension Gardener Handbook, Chapter 3: Botany, NC State Extension

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Correct answer: B. Its seeds are not enclosed in a fruit (ripened ovary)

Gymnosperms produce seeds that are not contained in a ripened ovary, while angiosperms enclose their seeds in a fruit. The smelly 'fruit' of a female ginkgo is really a seed with a fleshy covering, so ginkgo is a gymnosperm despite its broad leaves. The other choices are true of ginkgo, but being deciduous or having separate male and female trees also occurs in many angiosperms, so those traits do not define the group.

• A: Ginkgo is deciduous, but so are many angiosperms; leaf drop does not define gymnosperms.
• C: Separate male and female trees also occur in angiosperms such as hollies, so this does not define gymnosperms.
• D: Vein pattern is a useful identification feature, but it is not what separates gymnosperms from angiosperms.

Sources: Extension Gardener Handbook, Chapter 3: Botany, NC State Extension ; Ginkgo, The Morton Arboretum

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Correct answer: C. Maples, ashes, dogwoods or buckeyes

Paired leaves and buds mean an opposite arrangement, which most trees do not have. A tree with opposite leaves is very likely a maple, ash, dogwood or buckeye (horsechestnut), a group many students remember as 'MAD Cap Horse' (the 'Cap' stands for the honeysuckle family). Oaks, hickories, walnuts, elms, birches, cherries, lindens and honeylocusts all have alternate leaves.

• A: Oaks, hickories, walnuts and elms all have alternate leaves.
• B: Birches, cherries, lindens and honeylocusts all have alternate leaves.
• D: These conifers bear needles singly or in bundles, not opposite pairs of broad leaves with buds.

Sources: Basics of Tree ID: Leaf Arrangement, Virginia Tech Department of Forest Resources and Environmental Conservation ; Deciduous Trees in Winter (Plant Taxonomy BIOL 308 lab), College of Saint Benedict and Saint John's University, Department of Biology

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Correct answer: D. An axillary bud, found at the base of a whole leaf but not a leaflet

Buds form in the axil where a whole leaf joins the stem, so an axillary bud marks the true base of a leaf. Leaflets attach to the rachis of a compound leaf and have no buds at their bases, which is why a single leaflet is easily mistaken for a simple leaf. Stipules sit at the base of a whole leaf's petiole, not at the base of leaflets, so they do not mark a leaflet.

• A: Stipules, when present, sit at the base of the whole leaf's petiole or on the stem node, not only at leaflets.
• B: Lenticels are small corky pores on twigs and bark, not markers of leaflet attachment.
• C: Leaf scars form on the twig where a whole leaf falls, not on the rachis.

Sources: Extension Gardener Handbook, Chapter 3: Botany, NC State Extension ; Basics of Tree ID: Leaf Type, Virginia Tech Department of Forest Resources and Environmental Conservation

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Correct answer: D. Sweetgum (Liquidambar styraciflua)

Sweetgum's fruit is the spiny 'gumball,' a woody ball of many capsules that release seeds through openings in the surface. American sycamore also holds ball-shaped fruits into winter, which makes it the likeliest mix-up, but its balls are made of tiny winged achenes and are not spiny. Kentucky coffeetree bears thick, leathery pods, and northern catalpa bears long, bean-like capsules.

• A: Sycamore's fruit is a ball of tiny winged achenes and is not spiny.
• B: Kentucky coffeetree produces flat, thick, leathery pods.
• C: Northern catalpa produces long, slender, bean-like capsules.

Sources: Basics of Tree ID: Fruit, Virginia Tech Department of Forest Resources and Environmental Conservation ; Virginia Tech Dendrology Fact Sheet: sweetgum (Liquidambar styraciflua), Virginia Tech Department of Forest Resources and Environmental Conservation

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Correct answer: A. Chlorophyll in the bark, which lets the branches and trunk carry on photosynthesis

Paloverde's tiny leaves are drought deciduous, dropping when conditions turn unfavorable, but the tree keeps photosynthesizing because its branch and trunk bark contains chlorophyll. This green, photosynthetic bark is a key desert adaptation and a handy identification feature. The color comes from the bark tissue itself, not from a wax coating, a lichen or stored water.

• B: The green color comes from chlorophyll that supports photosynthesis, not from a reflective wax.
• C: The green color is chlorophyll in the bark itself, not a lichen covering.
• D: The green bark works in photosynthesis; it is not a succulent water-storage tissue.

Sources: Trees and Shrubs, Saguaro National Park, National Park Service ; Trees and Shrubs, Saguaro National Park, National Park Service

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Correct answer: B. The average annual extreme minimum winter temperature

The USDA map divides the country into zones by the average annual extreme minimum winter temperature, in 10-degree F zones with 5-degree F half zones (a and b). It reflects the average lowest winter temperatures over a 30-year period, not the coldest temperature ever recorded. Frost dates, summer heat and precipitation also affect plant success, but they are not what the zones measure.

• A: Frost dates are not the basis of the USDA hardiness zones.
• C: Summer heat is a separate factor that the hardiness zones do not measure.
• D: Precipitation is not part of the hardiness zone calculation.

Sources: 2023 USDA Plant Hardiness Zone Map, USDA Agricultural Research Service ; How to Use the Maps, USDA Agricultural Research Service

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Correct answer: D. Pin oak (Quercus palustris)

Pin oak suffers greatly from leaf chlorosis caused by high soil pH, which can lead to serious decline, so The Morton Arboretum no longer recommends it where soil pH is high. Kentucky coffeetree and hackberry tolerate high pH, and bur oak, the most tempting distractor because it is also an oak, is adaptable to many soils, including alkaline ones. Testing soil pH before choosing species is what reveals this kind of mismatch.

• A: Kentucky coffeetree is tolerant of high soil pH.
• B: Hackberry is pH tolerant and grows well on many difficult sites.
• C: Bur oak is adaptable to many soils, including alkaline soils.

Sources: Pin oak, The Morton Arboretum ; Pin oak, The Morton Arboretum ; Kentucky coffeetree, The Morton Arboretum

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Correct answer: B. Eastern redbud (Cercis canadensis)

Under wires, choose a short flowering tree whose mature height stays below the lines; eastern redbud is a large shrub or small tree that grows to about 30 feet. London planetree, tuliptree and eastern white pine all become large trees that grow far taller than utility lines. Planting large trees beneath utility lines leads to repeated clearance pruning and disfigured crowns.

• A: London planetree is a very large tree that can reach about 100 feet.
• C: Tuliptree often grows over 100 feet tall.
• D: Eastern white pine often grows well over 100 feet tall.

Sources: Tree City USA Bulletin No. 4: The Right Tree for the Right Place, Arbor Day Foundation ; Virginia Tech Dendrology Fact Sheet: eastern redbud (Cercis canadensis), Virginia Tech Department of Forest Resources and Environmental Conservation ; Tree City USA Bulletin No. 4: The Right Tree for the Right Place, Arbor Day Foundation

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