Authors: TunyaLee Morisawa, Global Invasive Species Team, The Nature Conservancy
- Phellodendron amurense is a perennial tree that can grow from 35-45 ft. (10-14 m) tall. The tree has a short trunk with spreading branches. The bark is thick and corky.
- Leaves are opposite, compound (divided into 5-11 leaflets) and 10-15 in. (25-38 cm) long. Leaflets are elliptical, acute at the apex, 2.5-4.5 in. (6-11 cm) long and smell like turpentine when crushed.
- Flowering occurs in late spring, when bunches of small, green flowers develop.
- Fruits are drupes, 0.25-0.5 in. (0.6-1.3 cm) in diameter and bright green (black when mature).
- Ecological Threat
- This tree is demonstrating invasive characteristics in suburban and urban fringe forests. It escapes intended plantings to invade and displace native hardwood forest. Note: only female plants have potential to become invasive. Phellodendron amurense is native to eastern Asia and was introduced into the United States in 1856. Trees prefer full sun and rich soils.
The landscape tree Phellodendron amurense Rupr. was introduced into the USA from eastern Asia sometime prior to 1874. Unfortunately, this tree is demonstrating invasive characteristics in suburban and urban fringe forests in New York state and Pennsylvania. This tree is popular as a landscape ornamental. Such frequent use will give it many opportunities to escape from cultivation.
Phellodendron amurense Rupr. (Rutaceae--citrus family) is a deciduous tree which reaches heights of 9-12 m. Mature specimens have short trunks with deeply ridged and corky bark, and widely spreading crowns. The leaves are dark green (yellow in the fall) and 23-38 cm long. The compound (odd-pinnate) leaves consist of 5-13 leaflets. Male and female flowers occur on separate trees. The inconspicuous, green-yellow flowers bloom in June. Clusters of fleshy, black berries remain on the trees into the late fall and winter. Each berry is 8-12 mm wide, and contains five seeds.
Phellodendron amurense is very similar in appearance to P. japonicum Maxim. (Japanese cork-tree), P. lavallei Dode (cork-tree), and P. sachalinense (F.Schmidt) Sarg. (cork-tree). The nursery industry has produced a number of male-only cultivars, including Phellodendron 'His Majesty' and Phellodendron 'Macho' . These cultivars can pollinate female P. amurense plants.
Phellodendron amurense has been observed aggressively invading suburban and urban fringe forests. The tree has the following characteristics:
1) Phellodendron amurense is adaptable to various environmental conditions; it grows well in different soil types (clays to light sand), is pH adaptable, drought tolerant, and has no serious pest problems.
2) In areas with ample moisture and good soil, the tree produces large amounts of seed.
3) Phellodendron amurense quickly invades disturbed forest areas.
Phellodendron amurense is native to eastern Asia (northern China, Manchuria, Korea, Ussuri, Amur, and Japan).
As a non-native, Phellodendron amurense is heat-loving, cold-tolerant, and hardy in USDA zones 4-7. It is used throughout the southeastern USA, from the coast inland towards the mountains. Although the literature states that this tree is adaptable to many types of environmental situations, field evaluations have demonstrated that its performance as a landscape tree is unreliable in some environments. During trials in Kansas, the tree initially performed well but suffered from winter die-back. Furthermore, its foliage often scorched during the summer, and overall quality was poor. Specimens from Japan planted in north central USA survived well the first year, but most died within 10 years. In contrast, three trees survived very well in Ohio.
North of Philadelphia (in Montgomery County, Pennsylvania) P. amurense has aggressively invaded disturbed forests. It has been observed escaping into native hardwood forests in New York. By preventing the regeneration by native species, the oak-hickory hardwood forests become transformed into Phellodendron forests.
Control methods have not been developed for this relatively new invader. Considerations for a control program would include:
1) Focus on reducing or stopping fruit production and spread. When allocating limited resources in a control program, it might be appropriate to concentrate control efforts on female plants.
2) Practice disturbance prevention. Phellodendron amurense easily invades disturbed areas.
Virginia Tech Department of Forest Resources and Environmental Conservation 
University of Connecticutt Database of Trees, Shrubs and Vines 
Ralph A. Read and John C. Zasada, Woody Plant Seed Manual 
Plant Conservation Alliance's Alien Plant Working Group 
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USDA NRCS PLANTS 
USDA ARS GRIN 
Breen, P. 1999, Oregon State University, Personal communication.
Glen, S. 1996, New York Metropolitan Flora News 1:2, Brooklyn Botanic Gardens (broken link).
Jacobson, A.L. 1996, North American Landscape Trees. Ten Speed Press, Berkeley California p. 423.
Rhoads, A. 2000, Director, Pennsylvania Flora Project at the Morris Arboretum. Personal communication.
Syrett, C. 2001, Forest Manager at Forest Park, Queens, New York, Personal communication.
Images from Bugwood.org