Phellodendron, commonly known as cork-tree, is a genus of deciduous, dioecious trees in the family Rutaceae (order Sapindales), native to east and northeast Asia. The genus is characterised by leathery, pinnately compound leaves, small yellow flowers borne in clusters, and black drupes that ripen in late autumn. In several species — most notably Phellodendron amurense, the Amur cork-tree — the bark is strikingly thick and deeply furrowed, resembling the bark of the unrelated cork oak (Quercus suber), though it is not thick enough for commercial cork production. The genus name combines the Greek phellos (cork) and dendron (tree), referencing this distinctive bark.
In cultivation, Phellodendron is valued as a four-season ornamental: spring brings pale yellow flowers, summer offers dense foliage and shade, autumn foliage turns bright yellow, and the sculptural branching and textured bark provide winter interest. The trees are hardy to USDA zone 4, tolerant of drought and poor soils, and largely free of serious pests. However, P. amurense in particular has become an invasive concern in the mid-Atlantic and New England regions of the United States: its sugar-rich fruit is eagerly dispersed by birds and mammals, and the allelopathic seedlings can suppress native hardwood regeneration, allowing the species to dominate disturbed forest understories.
Phellodendron amurense has long been used in traditional Chinese medicine — it is listed among the 50 fundamental herbs — where the dried bark (huáng bǎi or huáng bò) is the principal medicinal part. The bark contains several bioactive alkaloids, including berberine, jatrorrhizine, phellodendrine, and palmatine, which are subjects of ongoing pharmacological research. The bark has also historically been used as a source of yellow dye.
Etymology
The genus name Phellodendron derives from the Greek phellos (cork) and dendron (tree), a reference to the thick, deeply furrowed, cork-like bark found in several species, especially P. amurense. The common name "cork-tree" reflects the same character, though the genus is unrelated to the true cork oak.
Distribution
Phellodendron is native to east and northeast Asia. P. amurense, the best-known species, occurs in northern China and in the Khabarovsk and Primorsky regions of the Russian Far East. The genus has been widely introduced as an ornamental elsewhere, and P. amurense is now considered invasive or of invasive concern in parts of eastern North America, particularly the mid-Atlantic states and New England.
Ecology
The black drupes produced by female trees are rich in sugars and attract birds and mammals throughout late autumn and winter, facilitating wide seed dispersal. Phellodendron amurense is of particular ecological concern in eastern North America, where dense seedling establishment and allelopathic effects can suppress the reproduction of native hardwood species, potentially allowing the cork-tree to dominate forest understories under favorable conditions.
Cultivation
Phellodendron is hardy to USDA zone 4 and tolerates drought, varied soils, and most common pests and diseases, making it low-maintenance in most temperate gardens. Trees are dioecious; planting male cultivars (such as P. amurense 'His Majesty') avoids the inconvenience of fruit drop on lawns and reduces invasive spread. In many jurisdictions, planting P. amurense outdoors is now discouraged or regulated due to its invasive potential.
Cultural Uses
The bark of Phellodendron amurense is one of the 50 fundamental herbs of traditional Chinese medicine, known as huáng bǎi (黄柏) or huáng bò (黄檗), and is used primarily for its bitter, heat-clearing properties. The bark has also been used as a source of yellow dye. Pharmacological interest centres on the alkaloids berberine, jatrorrhizine, phellodendrine, and palmatine, which show antibacterial, antifungal, and other biological activities in early laboratory studies; clinical applications remain under investigation.
