On your next visit to the parks, we challenge you to find these five trees that are rooted there. And if you missed the first part of this blog, get the other half of this list here!
The twisted upper branches and deeply furrowed bark of the black locust (Robinia pseudoacacia) gives this tree a unique silhouette. A host plant for clouded sulphur butterflies and silver-spotted skippers, black locust is considered an invasive in some parts of the United States, particularly where it has begun to colonize dry prairies and savannas.
Black locus trees aren't typically tall, but have been known to grow up to 100 feet tall. Notice their compound leaves with 7 to 19 leaflets on one stem, all of them paired except for the end leaflet. They are smooth and oval-shaped, and droop at night. Locust fruits are dark brown pods up to four inches long.
Black locust make themselves unappetizing to deer by growing intimidating-looking thorns, which occur on new growth.
Like black cherry, black locust is an early succession species, a site colonizer. Wherever it’s growing, it’s making that site more suitable for other dominant trees like oaks and maples.
The yellow buckeye (Aesculus flava) is a close relative of the Ohio buckeye (Aesculus glabra). How can you tell the difference? Both trees have an unpleasant odor, but the Ohio buckeye’s is more pungent; yellow buckeyes are larger; and the stamen of the Ohio buckeye flowers are much longer.
Yellow buckeye leaves have five distinct leaflets, similar to the horse chestnut, which is in the same tree family. (The leaf buds of the horse chestnut are very sticky, which is a helpful way to distinguish them.) The yellow buckeye’s flowers are yellow and form upright clusters. The fruit, a smooth nut enclosed in a thick husk, is poisonous to humans but a delicacy for squirrels.
A helpful memory trick that our educators use to identify buckeyes is MAD BUCK. "MAD" stands for maple, ash, and dogwood, "BUCK" for buckeye. These four types of trees are the only ones in our area that have opposite leaves. (Note: Since buckeyes are in the same family as the horse chestnut, you could also say MAD HORSE.)
White oaks (Quercus alba), despite not being extraordinarily tall, often project a massive appearance thanks to low branches that are parallel to the ground. White oaks can grow as wide as they are tall, giving them a distinctive silhouette. They have a light gray bark that peels slightly, and glossy green leaves that are lobed and oval in shape. In the spring, leaves are downy and silvery pink.
The white oak is an excellent shade tree because of its wide branching and its tendency not to drop its limbs. It grows well in almost all soils except those that are particularly dry and shallow. They are fairly slow-growing compared to other oaks, but they tend to have long life spans.
White oaks have rounded leaf lobes and their acorns ripen within one season.
White oaks are somewhat resistant to oak wilt disease. They will contract the disease but they generally do not have fatal symptoms, unlike red oaks. Like red oaks, white oaks are also a group—white oak, swamp white oak, and bur oak are the most common. To date, wherever oak wilt has been controlled in the parks, we have removed the white oaks as well as the red oaks, knowing that the white oak could be a host for future infections of red oaks.
When trying to distinguish the native staghorn sumac and the invasive tree of heaven (Ailanthus altissima), remember that "fuzzy is a friend." It's quite hard to tell which tree is which, until you notice that sumacs have fuzzy stems, while tree of heaven has a smoother bark. The tree of heaven is also distinguished by a rancid odor that is released when the leaves are crushed or rubbed. (In the tree’s native China, its name is chouchun, or “malodorous tree.”)
Introduced to the United States in the 1700s as an ornamental, it was heavily planted as a street tree because it can grow in harsh conditions. It has escaped cultivation and moved heavily into natural areas, where it has been extremely destructive to native plants. The tree thrives in full sun and disturbed areas, so it’s quick to populate a canopy gap, where (like the Norway maple) it adds to its destructive effect by releasing toxins into the soil that inhibit the growth of other plants.
Tree of heaven is one of the fastest-growing trees in North America, shooting up between 3 and 7 feet per year for the first four years of its life.
Nicknamed the Pittsburgh palm, our city embraced tree of heaven as a horticultural plant around the Industrial Revolution. After so much environmental degradation, it was one of the few tree species that really thrived. But today, there is a need to control the spread of this plant. It, along with Norway maples, exudes herbicides from its roots and excludes our native trees, shrubs, and flowers from growing.
Witch hazel (Hamamelis virginiana) is a small, shrubby tree, well-suited to the understory. Its scientific name Hamamelis means “together with fruit,” which refers to the fact that its fruit, flowers, and leaf buds all appear at the same time (making it unique among trees native to North America).
The list of remedies that use witch hazel is pretty long, from acne to psoriasis, insect bites to blisters. Witch hazel can really add a pop of color to parks in the cold months as its thread-like yellow flowers bloom in late fall and winter. In springtime the small buttons that contain the seed pods burst and shoot out the seeds that have been ripening over the past year.
Witch hazel is a great native plant that blooms during the winter when nothing else blooms. It does best in wet, riparian areas, but it is adaptable. It’s a smaller tree, usually multi-stemmed.
This blog has been adapted from the series Top 15 Trees in the Parks. Check out the series start here!