AppearanceIt is a dense, deciduous, spiny shrub which grows 0.6 to 2.5 m high. It has deeply grooved, brown, spiny branches with a single spine at each shoot node. The leaves are green to blue-green , very small, spatula to oval shaped, 12–24 mm long and 3–15 mm broad; they are produced in clusters of 2-6 on a dwarf shoot in the axil of each spine. The flowers are pale yellow, 5–8 mm diameter, produced in drooping 1-1.5 cm long umbrella-shaped clusters of 2–5; flowering is from mid spring to early summer. The edible fruit is a glossy bright red to orange-red, ovoid berry 7–10 mm long and 4–7 mm broad, containing a single seed. They mature during late summer and fall and persist through the winter.This species is sometimes confused with ''Berberis canadensis'' , ''Berberis vulgaris'' , and other deciduous ''Berberis'' species; it is most readily distinguished by the flowers being produced in umbels, not racemes.
NamingIn recent years, ''Berberis thunbergii'' has been recognized as an invasive species in many parts of the eastern United States. The Plant Conservation Alliance's Alien Plant Working Group lists it among its "Least Wanted".
This ''Berberis'' is avoided by deer, and has been replacing native species. Furthermore, the plant can raise the pH of the soil and affect soil nitrogen levels. Unlike ''B. canadensis'' and ''B. vulgaris'', ''B. thunbergii'' does not act as a host for ''Puccinia graminis'' , a rust disease of wheat. It is also an exceptionally favorable environment for ticks.
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