Shrubs, evergreen, 0.3-3(-4.5) m. Stems usually monomorphic, seldom with short axillary shoots. Bark of 2d-year stems gray-brown or purplish, glabrous. Bud scales 4-8(-14) mm, deciduous. Spines absent. Leaves 5-9-foliolate; petioles 1-6 cm. Leaflet blades thin and flexible or rather rigid; surfaces abaxially glossy, smooth, adaxially glossy, green; terminal leaflet stalked, blade 5.1-8.7(-14.5) × 2.4-4.5(-5.5) cm, 1.7-2.5 times as long as wide; lateral leaflet blades lance-ovate to lance-elliptic, 1(-3)-veined from base, base obtuse or truncate, rarely weakly cordate, margins plane or undulate, toothed, each with 5-21 teeth 0-2 mm tipped with spines to 0.8-2.2 × 0.2-0.3 mm, apex acute or sometimes obtuse or rounded. Inflorescences racemose, dense, 30-60-flowered, 3-9(-11) cm; bracteoles membranous, apex rounded or obtuse, sometimes apiculate. Flowers: anther filaments with distal pair of recurved lateral teeth. Berries blue, glaucous, oblong-ovoid, 6-10 mm, juicy, solid. 2n = 28, 56.
Phenology: Flowering winter–spring (Mar–Jun).
Habitat: Open woods and shrublands
Elevation: 0-2100 m
B.C., Calif., Idaho, Mont., Oreg., Wash.
Berberis aquifolium is the state flower of Oregon. It is widely used as an ornamental and has been reported as an escape from cultivation in scattered localities across the continent (Ontario, Quebec, central California, Michigan, and Nevada).
Berberis aquifolium is resistant to infection by Puccinia graminis.
Medicinally, various root preparations of Berberis aquifolium were used by Native Americans for stomach trouble, hemorrhages, and tuberculosis; as a panacea, a tonic, a gargle, and an eye wash; and to purify blood. Leaves and roots were used in steam baths to treat yellow fever; karok was used as a poison; and the tips of stems were used to treat stomach aches (D. E. Moermann 1986).