Pl. Nouv. Amér., 113. 1841.
Shrubs, evergreen, 1-3.5 m. Stems ± dimorphic, with elongate primary and short axillary shoots. Bark of 2d-year stems gray or grayish purple, glabrous. Bud-scales 2-3 mm, deciduous. Spines absent. Leaves 3-foliolate; petioles 0.8-5.4 cm. Leaflet blades thick and rigid; surfaces abaxially dull, papillose, adaxially dull, ± glaucous; terminal leaflet sessile, blade 2.3-5.8 × 0.9-2 cm, 1.6-3.1 times as long as wide; lateral leaflet blades narrowly lanceolate or narrowly elliptic, 1-veined from base, base acute or acuminate, rarely rounded-acute, margins plane, toothed or lobed, with 1-3 teeth or lobes 3-7 mm high tipped with spines to 1-2 × 0.2-0.3 mm, apex narrowly acute or acuminate. Inflorescences racemose, lax, 1-8-flowered, 0.5-3 cm; bracteoles membranous, apex acuminate. Flowers: anther-filaments without distal pair of recurved lateral teeth. Berries red, sometimes glaucous, spheric, 6-11 mm, juicy, solid.
Phenology: Flowering winter–spring (Feb–Apr).
Habitat: Slopes and flats in grassland, shrubland, and sometimes open woodland
Elevation: 0-2000 m
Ariz., N.Mex., Tex., n Mexico
The illegitimate name Berberis trifoliolata Moricand var. glauca (I. M. Johnston) M. C. Johnston has been used for plants with very strongly glaucous leaves. Weakly and strongly glaucous plants are often found in the same population, however, indicating that they are not distinct varieties.
Berberis trifoliolata is susceptible to infection by Puccinia graminis.
"thick" is not a number.