Japanese barberry (Berberis thunbergii) is a perennial deciduous shrub native to Japan, now considered a serious invasive in the United States. It is one of about 500 in the genus. This plant was sent from eastern Russia to the Arnold Arboretum in 1875 as a potential ornamental with notable autumn coloration for settlers in New England (Swearingen 2005; Wikipedia 2013). When the European barberry (B. vulgaris), another introduced species widespread in the United States, was found to host the destructive grain fungus black stem grain rust (Puccinia graminis f. sp. tritici), a long federal and state B. vulgaris eradiation campaign began in 1918 and the USDA encouraged planting of the closely related Japanese barberry as a fungus-resistant and attractive substitute to B. vulgaris (USDA Agricultural Resource Service 2010; Swearingen 2005). As a result, Japanese barberry now grows throughout the northeastern United States as far west as western North and South Dakota and is still spreading west (Zouhar 2008).
A very adaptable drought- and shade-resistant plant with very low rates of mortality, B. thunbergii grows in a range of habitats from open fields and meadows to wetlands to deep shaded forest, growing up to 8 feet (2.5 m) high, often in dense impenetrable thickets (Grebenstein 2013; Swearingen 2005; Ehrenfeld 1999). Its prolific and readily germinating bright red berries are widely spread by birds and small mammals, but white-tailed deer avoid eating the plant, giving it a competitive advantage over native species, which it easily and completely displaces. In addition to growth from seed, the branches of B. thunbergii root when they touch the ground and root fragments readily sprout to form new individuals, so it is persistant difficult to remove once established. As well as altering native wildlife habitat, Japanese barberry changes the ecology around it by raising the soil pH, altering nitrogen levels and biological activity in the ground, and reducing leaf litter depth in forests (Swearingen 2005; Kourtev et al. 1999; Silander and Klepeis 1999). The Plant Conservation Alliance’s working group lists it as one of the least wanted alien plant invaders of natural areas and recommends against planting it, however it has many popular cultivars and nurseries in the US commonly sell it for landscaping purposes (Swearingen 2005).