Growing Together: Test your tree IQ
I’m glad I’m not a worrier. With all the news reports of deadly tree pests headed our way, it’s enough to make one lie awake nights stressing about landscape plants.
Much of the anguish can be lessened if we know our tree types. If you’re alarmed about emerald ash borer, oak wilt and black knot, you have nothing to fear if you realize your trees are hackberry.
Identifying tree types is easiest by learning leaf shapes. A drive along streets in newer developments shows the wide diversity being planted – quite a change from the continuous rows of elm and ash gracing the streets of older neighborhoods.
Following are the common trees encountered in our yards and along boulevards with a few distinguishing leaf characteristics.
1. Green ash and its many named varieties were the shade tree most commonly planted during the past 40 years as the answer to Dutch elm disease.
Unfortunately, now the emerald ash borer has killed millions of trees since it was identified in 2002. It has spread through the eastern United States, and has progressed as close as Minneapolis-St. Paul and Duluth-Superior.
Green ash has a compound leaf. If you detach a leaf at the natural break-away point where the leaf joins the twig, you’ll see it’s composed of leaflets, usually seven in number. Leaflets are dark green, smooth and glossy.
2. Fallgold black ash is similar to green ash, except leaf color is a lighter shade of green, more yellowish underneath, and duller. The leaf consists of seven to 13 leaflets. Buds along the twigs are distinctly dark brown to black.
3. Black walnut leaves are compound with an average of 15 leaflets, making the entire leaf usually over 10 inches long. Leaflets are pointed ovals about 3 inches long.
4. Elm is recognized by its classic upward arching “vase” shape, which is visible as you view tree-lined streets in older neighborhoods. Recent varieties of disease-resistant elm are being planted along boulevards.
Elm leaves are “simple” meaning they are born singly along twigs, without leaflets. Leaves tend to feel rough. They are doubly serrated, meaning they have both long and short teeth along the margin. The base of the leaf is lop-sided rather than straight across.
5. Hackberry leaves look a little like elm, lop-sided at the base, but hackberry leaf edges are not doubly-toothed. Margins are serrated singly instead.
6. Birch is usually an easy give-away because of its white or copper bark. Leaf bases are straight across, rather than lopsided like elm and hackberry.
7. Bur oak is a familiar leaf-shape with lobes that are rounded. Bur oak is a North Dakota native, and is distinguishable from Minnesota’s red oaks and pin oaks, which have sharply pointed leaf lobes.
8. Silver maple received its name from the leaves’ whitish undersides. Maple leaves are the shape made famous by Canada’s flag, except the lobes of silver maple are deeply cut almost to the center midrib. Silver maple often shows yellowing from iron chlorosis.
9. Sugar maple leaf lobes are not cut as deeply toward the center as silver maple. Fall colors are terrific with orange, red and gold tones.
10. Norway maple leaves are deep green and broad, often with seven lobes instead of silver and sugar maple’s five. Detaching a leaf from a twig produces a drop of milky sap.
11. Boxelder foliage tends to be slightly yellow-green. Leaves are compound with three to five leaflets.
12. Honeylocust foliage is almost fernlike because the leaves are doubly compound. That means the leaves are divided into leaflets, and the leaflets are further divided into even smaller ovals.
13. Cottonwood is a member of the poplar genus. Modern hybrid poplars are often called “cotton-less cottonwoods.” Leaves are broadly triangular, waxy and glossy.
14. Columnar aspen and its cousin quaking aspen are both poplars with rounded leaves with coarse teeth around the margin. Shiny waxiness makes leaves rustle pleasantly in the breeze.
15. Lindens are easily recognized by their pyramidal shape. The American linden, also known as basswood, becomes broad-spreading with age. Others, like Redmond linden, retain a definite lifelong pyramidal form.
Linden leaves are rounded, coming to a point, with lopsided bases. Round seeds with attached yellowish wings contrasted with dark green foliage give linden trees a two-tone appearance in mid-summer.
16. Canada red cherry is the most common purple-foliaged tree region-wide. It is also known as Schubert chokecherry, shorter in stature than large shade trees like elm and ash. Purple-black, pea-sized fruits are edible and used the same as green-leaved chokecherry. Birds usually beat us to them.
17. Willows of the weeping type are familiar with their gracefully hanging branches. Other varieties are upright and round-spreading.
Now that we can recognize leaves, identifying trees from a distance by overall shape and texture is a fun challenge. If done while in a vehicle, a designated driver is a good idea.