Amur corktree (Phellodendron amurense)

Synonyms: Phellodendron amurense var. amurense

Common Names: Amur cork tree, Chinese corktree, Sakhalin corktree

Description:

Amur corktree (Phellodendron amurense) is a medium-sized deciduous tree from eastern Asia that was brought to the United States in the 1850s as an ornamental and street tree [1][2]. It has escaped from plantings and now invades hardwood forests and edges, mostly in the northeastern and midwestern United States [2][3]. MISIN tracks it because it casts dense shade, replaces native hardwood trees, and spreads quickly as birds carry its black fruit into the woods [2][3].

Habit:

Amur corktree is a broad, often flat-topped tree that grows about 30 to 50 feet tall [3]. Its bark is its giveaway: ridged, deeply furrowed, and spongy or corky to the touch, and if you cut into it the inner bark is bright yellow ? a trait no native look-alike shares [2]. The leaves are arranged in pairs (opposite) and are compound, 10 to 15 inches long, with 5 to 11 pointed leaflets; crushed leaves smell of citrus or a faint disinfectant [2]. Opposite compound leaves are unusual among trees, which helps narrow it down [2].

You can identify it year-round by the corky bark and yellow inner bark. In late summer and fall, female trees carry clusters of round black fruit, and the citrus-scented leaves are easiest to check spring through fall [2]. Male and female flowers grow on separate trees, so only female trees bear fruit [2].

At-a-glance cues:

1. Ridged, corky, spongy bark with bright yellow inner bark when cut [2]
2. Opposite, compound leaves (5?11 leaflets) that smell of citrus when crushed [2]
3. Round black fruit in clusters on female trees in late summer and fall [2]
4. Broad, flat-topped tree about 30?50 feet tall [3]

Leaves:

1. Arranged in pairs (opposite) along the twig ? unusual for a tree [2]
2. Pinnately compound, 10?15 inches long, with 5?11 leaflets [2]
3. Leaflets 2?4? inches long, pointed, with smooth (untoothed) edges [2]
4. Crushed leaves smell of citrus or a faint disinfectant [2]

Stems:

1. Woody tree, about 30?50 feet tall, with a broad, often flat-topped crown [3]
2. Bark is ridged, deeply furrowed, and spongy or corky to the touch [2]
3. Inner bark is bright yellow when cut ? a key identifying trait [2]
4. Cut stumps and roots resprout readily [2]

Flowers:

1. Small and yellow-green, borne in branched clusters [2]
2. Male and female flowers grow on separate trees (dioecious), so only female trees set fruit [2]
3. Bloom in late spring to early summer [2]

Fruit and seeds:

1. Fruit is a round, berry-like drupe about ? inch (1 cm) across, borne in clusters on female trees [2]
2. Ripens from green to black or purplish-black in late summer and fall and often persists into winter [2]
3. Aromatic; birds eat the fruit and spread the seeds widely [2]
4. Seeds can stay viable in the soil for several years [2]

Habitat:

Amur corktree grows in forests and along forest edges, in floodplains, old fields, and disturbed areas, and it lingers around yards and streets where it was planted [2][3]. It tolerates shade and a range of soils, which lets it move into intact woodlands as well as open ground [2].

The tree is native to eastern Asia ? China, Korea, Japan, and the Russian Far East [1]. It was introduced to the United States in the 1850s as an ornamental and is now naturalized across parts of the northeastern and midwestern United States [1][2].

Reproduction:

Amur corktree spreads by seed, and birds are the main carriers. They eat the black fruit from female trees and drop the seeds far away, including deep into the woods and along edges [2]. It also spreads from trees that people planted as ornamentals or street trees [2]. So it can arrive as a bird-dropped seedling or spread from an old planted tree nearby.

Only female trees bear fruit, but a single female near other corktrees can produce a heavy seed crop, and the seeds stay viable in the soil for several years [2]. Cut trees resprout from the stump and roots, so simply cutting one down does not kill it [2]. The best control timing is to remove young plants early, before female trees begin to fruit, to stop new seed from spreading [2].

Impact and Damage:

Amur corktree is not known to harm people or pets. Its damage is to forests and the native plants in them. It grows into the forest canopy and casts dense shade, which makes it hard for native tree seedlings, shrubs, and wildflowers to grow beneath it [2][3]. Over time it can replace native hardwood trees and take over the understory of a woodland [2][3].

For natural area stewards, the concern is that it establishes inside otherwise healthy forests, not just on disturbed ground, and birds spread its seed widely, so new trees can appear far from any planted source [2][3]. Because it tolerates shade, it can keep filling in under an existing canopy, gradually shifting a native forest toward corktree [2][3].

Similar species:

Ash trees (Fraxinus species) are the closest look-alike, because they also have opposite, compound leaves. Tell them apart by the bark and fruit: ash bark is ridged but not corky or spongy and has no bright yellow inner layer, and ash trees bear dry, winged seeds rather than black fruit [2]. Boxelder (Acer negundo) also has opposite compound leaves, but usually only 3?7 coarsely toothed leaflets, green twigs, and winged "helicopter" seeds [2].

Black walnut (Juglans nigra) has compound leaves that look similar, but they are arranged alternately (not in pairs), the many leaflets are toothed, and it bears large round nuts [2]. Tree-of-heaven (Ailanthus altissima) has large alternate compound leaves with a few rounded teeth near each leaflet base and a strong unpleasant smell, and it has neither corky bark nor yellow inner bark [2].

Monitoring and rapid response:

Signs to watch for:

1. Medium trees with ridged, corky, spongy bark and bright yellow inner bark when cut [2]
2. Opposite, compound leaves that smell of citrus when crushed [2]
3. Clusters of round black fruit on female trees in late summer and fall [2]

What you can do:

1. Pull or dig out seedlings and small saplings when the soil is moist, getting as much of the root as you can [2].
2. Expect larger trees to resprout from the stump and roots if simply cut, so plan to dig the roots or repeat the work over time [2].
3. Focus on female (fruit-bearing) trees first, and bag and dispose of fruit before birds can spread the seed [2][3].
4. Act early ? remove young plants before they reach fruiting size [2].
5. Don't plant Amur corktree; choose a native tree instead.
6. Natural area crews should prioritize seed-producing female trees and scattered saplings, work across a site over repeat years since it resprouts and reseeds, and watch edges and floodplains where birds drop seed [2][3].

When to call a professional:

1. Large or mature trees, or stumps and roots that keep resprouting after cutting.
2. Sites where digging and cutting are not keeping the tree in check.
3. For chemical control options, contact a licensed applicator or your local cooperative extension office.

Report sightings to MISIN. Help track this species' spread by submitting observations through the MISIN web site or the MISIN mobile app (Android, iOS, Windows, and macOS). Photos at multiple angles paired with a precise GPS location are the most valuable data for confirming new occurrences and triggering rapid-response review.

Credits:

1. USDA NRCS Plants Database. Phellodendron amurense Rupr. plants.usda.gov
2. Penn State Extension. The Invasive Amur Corktree. extension.psu.edu
3. Minnesota Department of Natural Resources. Amur Cork Tree (Phellodendron amurense). dnr.state.mn.us
4. University of Minnesota Extension. Amur Corktree. extension.umn.edu
5. Wisconsin Department of Natural Resources. Amur Cork Tree (Phellodendron amurense). dnr.wisconsin.gov

---