The U.S. Department of Agriculture lists Berberis thunbergii as resistant to infection by Puccinia graminis , and the species is widely grown as an ornamental in the United States. Preliminary tests carried out by Agriculture Canada, however, suggest that some strains may be susceptible to Puccinia graminis infection, and cultivation of B . thunbergii is illegal in Canada.
Shrub 30 cm - 3 m tall Leaves: alternate, short-stalked, bright green, 1 - 3 cm long, 0.3 - 1 cm wide, spoon-shaped to narrow and inversely egg-shaped with a rounded to blunt tip, gradually tapering to the base, non-toothed, thin and flexible, with a very light whitish waxy coating (glaucous) beneath. Flowers: borne solitary or two to five on a 1 - 1.5 cm inflorescence, subtended by membrane-like bracts with pointed tips. The six yellow petal-like sepals fall soon after flowering, each of the six yellow petals has two basal glands, and each filament lacks a pair of curved lateral teeth. Fruit: a red berry, 7 - 10 mm long, elliptic to spherical, juicy. Twigs: yellowish or purplish red, becoming purple to brown in second year, grooved, usually with simple spines. Form: rounded, densely branched, with long branches and short lateral branchlets.
Similar species: Berberis aquifolium and Berberis repens both have leathery compound leaves and bluish black berries, and they lack spines and short lateral branchlets. Berberis canadensis and Berberis vulgaris both have three-parted spines and toothed leaves. In addition, B. canadensis is upright, sparingly branched and has notched petals, while B. vulgaris has a freely branched and arching form.
Flowering: April to May
Habitat and ecology: Introduced from Asia, this species has escaped from cultivation and is now common in pastured oak woods.
Occurence in the Chicago region: non-native
Notes: Cultivation of this species is illegal in Canada, as some strains may be suceptible to Puccinia graminis, the pathogen causing stem rust of cereal crops. However, the USDA lists the species as being resistant to the pathogen. Japanese barberry is commonly planted in home landscapes, but birds disperse the seeds into natural areas where the plants can invade and shade out native understory plants.
Etymology: Berberis is a Latinized form of the Arabian name for barberry. Thunbergii was named after 19th century Swedish botanist, Carl Peter Thunberg.
Densely and divaricately branched, to 2 m; spines usually simple; lvs obovate to spatulate, mostly obtuse, entire, short-petiolate; fls solitary or in umbel-like clusters of 2-4, 8 mm wide; fr 1 cm; 2n=28. Native of Japan, frequently escaped from cult. along roadsides and in thickets in our range. May.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
This shrub is much used as a hedge plant and for ornamental planting. Nieuwland reports it as an escape in St. Joseph County and I have found seedlings in our garden on several occasions. Since it is so commonly used, it will no doubt be found often as an escape where suitable conditions obtain.
Indiana Coefficient of Conservatism: C = null, non-native