The black locust tree, Robinia pseudoacacia, is a deciduous species native to parts of the eastern and central United States. This article provides guidance on how to identify this tree through its distinctive features and seasonal indicators.
Distinctive Bark, Leaves, and Thorns
The black locust tree has several unique physical characteristics. Its bark, particularly on mature trees, is dark gray to black, thick, and deeply furrowed with prominent ridges that often interlace to form diamond shapes. Younger branches may have smoother, greenish-brown bark.
The leaves are pinnately compound, with multiple smaller leaflets arranged along a central stalk. Each leaf measures 8 to 14 inches long and contains 7 to 23 oval or elliptical leaflets. These leaflets are dull green, 1 to 2 inches long, and have smooth margins, arranged alternately along the stem.
Sharp, paired thorns are present at the base of each leaf stalk or leaf scar on the twigs. These thorns can range from 0.5 to 2 inches in length.
Seasonal Indicators: Flowers and Pods
Seasonal changes reveal additional identifying features. In late spring to early summer (April to June), the tree produces abundant, fragrant white flowers. These pea-like blossoms are arranged in hanging clusters, known as racemes, which can be 5 to 10 inches long. Often, the uppermost petal of each flower displays a small yellow spot. The flowers attract pollinators.
Following the bloom, the black locust develops seed pods. These pods are flat, smooth, and range in color from reddish-brown to dark brown or black. They are 2 to 4 inches long and contain several small, kidney-shaped seeds. The pods often persist on the tree through fall and winter, remaining visible after leaves have dropped.
Where to Find It: Habitat and Growth Patterns
The black locust tree is found in various environments due to its adaptability. It thrives in disturbed areas such as roadsides, forest edges, old fields, and pastures. While native to the eastern and central United States, particularly the Appalachian and Ozark Mountains, it has been widely planted and naturalized across North America, Europe, and Asia.
This tree exhibits a rapid growth rate, adding 2 to 4 feet in height annually. It reaches a height of 30 to 50 feet. The black locust forms dense thickets through root suckering, allowing it to spread aggressively and outcompete native vegetation. Its extensive root system also contributes to its use in erosion control.
Safety Considerations: Understanding Toxicity
While some parts of the black locust tree are utilized, its toxicity is important to note. Most parts of the tree, including the bark, leaves, seeds, and pods, contain toxic compounds such as robin and phasin. These substances can be harmful if ingested by humans or animals. The flowers are considered non-toxic or less toxic.
Symptoms of poisoning in humans can include nausea, vomiting, lethargy, and weakness. In animals, especially horses, ingestion can lead to depression, loss of appetite, abdominal pain, diarrhea, and in severe cases, paralysis or death. Avoid consuming any part of the black locust tree unless specifically prepared by experts.