Berberis thunbergii, the Japanese barberry, Thunberg’s barberry, or red barberry, is a species of flowering plant in the barberry family Berberidaceae, native to Japan and eastern Asia, though widely naturalized in China and North America. Growing to 1 m (3.3 ft) tall by 2.5 m (8.2 ft) broad, it is a small deciduous shrub with green leaves turning red in the autumn, brilliant red fruits in autumn and pale yellow flowers in spring. Numerous cultivars are available as ornamental plants suitable for hedging.
B. thunbergii has deeply grooved, brown, spiny branches with a single (occasionally tridentine) spine (actually a highly modified leaf) at each shoot node. The leaves are green to blue-green (reddish or purple in some horticultural variants), very small, spatula to oval shape, 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.