The Tree of Heaven (Ailanthus altissima) is a fast-growing deciduous tree, originally native to China and Taiwan, that has spread extensively worldwide. Its common name comes from the Moluccan name Ailanto, meaning “tree reaching for the sky.” It is recognized as a highly aggressive invasive plant, capable of rapidly colonizing disturbed landscapes, urban areas, and forest edges. Identifying its specific features is crucial for management, as it is often confused with native species like sumac and black walnut.
Identifying Features of the Leaves
The leaves are pinnately compound, consisting of multiple leaflets arranged along a central stalk, giving them a feather-like appearance. These large leaves can measure anywhere from one to four feet in length, containing between 11 and 41 individual leaflets.
The leaflets are lance-shaped and typically have smooth, or entire, margins. A distinct identification feature is the presence of one or two small, blunt teeth found only at the base of each leaflet. These basal teeth conceal a small, visually noticeable gland on the underside of the leaflet. This glandular tooth is a key differentiator from similar native trees, such as sumac, whose leaflets are usually toothed along their entire edge.
Bark, Trunk, and Branch Characteristics
On young trees and smaller suckers, the bark is thin, smooth, and may appear brownish-green or pale gray. As the tree matures, the bark transitions to a light gray color and develops a rougher texture with shallow, vertical fissures or streaks.
The mature bark is frequently described as resembling the textured skin of a cantaloupe, with light streaks running through the gray surface. The twigs are stout and lack a terminal bud. When a leaf falls, it leaves behind a large, prominent shield- or heart-shaped leaf scar. Breaking a twig reveals a large, spongy, light brown or tan center, known as the pith.
Distinguishing Reproductive Structures
This species is dioecious, meaning individual trees produce either male or female flowers. The flowers are small and yellowish-green, appearing in large clusters called panicles in late spring or early summer.
The fruit is a single-seeded, winged structure known as a samara. These samaras are produced in dense, hanging clusters. Each samara is typically one to two inches long, defined by its slightly twisted, propeller-like shape, which aids in wind dispersal. They start green, turn yellowish to bright red or orange in the summer, and then fade to brown as they persist into the winter months.
The Smell Test and Overall Growth Habit
One of the most reliable ways to confirm identification is through a sensory test, as all parts of the Tree of Heaven contain a strong, unpleasant odor. When the leaves or a twig are crushed, they release a smell commonly described as rancid peanut butter, burnt oil, stale popcorn, or cat urine.
This unique scent provides a quick, non-visual confirmation that distinguishes it from look-alike species, including sumac and black walnut. The Tree of Heaven frequently appears in dense clusters due to its prolific ability to reproduce not only by wind-dispersed seeds but also through root suckering. These root sprouts can emerge as far as 50 feet from the parent tree, allowing the species to quickly form thickets and thrive in challenging, disturbed environments like pavement cracks and urban alleyways.