Amur corktree is a medium-sized tree with a broad-spreading, rounded crown and dark green foliage.
Leaves are opposite, pinnately compound, up to 14 inches long, with 5–13 leaflets that are up to 4½ inches long, elliptical, with an acute tip; upper surface dark green, lower surface lighter. When bruised, the leaves emit a pungent odor similar to turpentine or citrus.
Bark on young trees is smooth and gray; with age, it becomes thick, deeply ridged, and corky. If the outer bark is scraped away, the inner bark is a distinctive, bright neon yellow.
Twigs are stout and orange-brown to gray, with large, horseshoe-shaped leaf scars.
Flowers May–June. Small yellow or yellowish-green flowers grow in upright clusters; male and female flowers occur on separate plants.
Fruits appear as clusters of pea-sized fleshy, round berries. They are green in summer, maturing to black in October. Each berry contains 1–5 seeds and can persist into the winter months.
Height: 30 to 50 feet.
Potentially found statewide. It was originally introduced as a landscape tree but has escaped cultivation in several urban areas, most notably around St. Louis.
Habitat and Conservation
This hardy species adapts to a wide variety of soil types, withstands heat and drought, tolerates cold, and resists pests. These characteristics make it attractive for landscaping, but it should not be planted. The qualities that allow it to survive here also contribute to its invasive nature. Female trees produce large quantities of seed that are widely dispersed by birds.
Male and female trees are easily distinguished in the fall, when female trees have clusters of black berries.
Status
Considered an invasive species in many parts of the United States. While it has not yet overtaken large forest tracts in Missouri, it is showing strong invasive tendencies in urban woodlands and riparian areas.
Human Connections
The species is named for its thick, corky bark, though it is not the source of commercial cork (which comes from the cork oak).
In addition to its use as a shade and landscape tree in North America, the Amur corktree has a long history in traditional Chinese medicine. The bright yellow inner bark contains berberine and has been used for centuries to treat various ailments. Despite these uses, its ecological impact in North America is overwhelmingly negative.
Ecosystem Connections
As corktrees increase in a forest, the diversity of native wildlife typically decreases. This species is a significant concern for forest managers because it can create dense stands that shade out native wildflowers and oak seedlings. It is a threat to native ecosystems because it displaces our native trees like oaks and hickories. These native species provide important, nutritious nuts (mast) that help wildlife survive winter. Compared to acorns and nuts, amur corktree berries, though abundant, do not provide the high-protein nutrition that birds and mammals require for winter survival.
