Trees or shrubs , evergreen, to 22 m. Bark nearly black, deeply furrowed with broad scaly ridges. Twigs brown to red-brown, 1.5-3 mm diam., glabrous or sparsely pubescent. Terminal buds light chestnut brown to dark reddish brown, ovoid to conic, 3-9 mm, glabrous or with tuft of minute hairs at apex. Leaves: petiole 3-20 mm, glabrous or sparsely pubescent. Leaf blade circular to oblong, usually ovate, planar, 25-70 × 20-50 mm, base obtuse to cordate, margins entire or spinose with up to 16 awns, apex acute to rounded; surfaces abaxially and adaxially glabrous, veins little raised on either surface. Acorns biennial; cup deeply and narrowly cup-shaped or U-shaped, 9-19 mm high × 7-18 mm wide, covering 1/3-1/2(-2/3) nut, outer surface glabrous to sparsely puberulent, inner surface glabrous or pubescent on innermost 1/3, occasionally uniformly pubescent, scales acute, tips loose; nut narrowly conic or ovoid to narrowly oblong, 21-44 × 8-14 mm, glabrous, scar diam. 2.5-7.5 mm. 2 n = 24. Flowering late spring. Valleys, slopes, and sand chaparral; 300-1900 m; Calif. Shrubs with oval leaves 25-38 mm and margins entire or deeply lobed-dentate may be treated as Quercus wislizenii var. frutescens . J. M. Tucker (1993) treated Q . parvula as a distinct species, distinguished from Q . wislizenii by its larger leaves (30-90 versus 20-50 mm), by the dull, olive-green, abaxial leaf surface (versus shiny, yellow-green), and by nuts that are abruptly tapered proximal to the middle (versus gradually tapered). Tucker recognized two varieties of Quercus parvula : Q . parvula var. parvula is a shrub of 1-3 m and Q . parvula var. shrevei is a tree less than 17 m. S. K. Langer (1993) recognized a third variety, Q . parvula var. tamalpaisensis ,based on several small populations on or near Mount Tamalpais, differentiated primarily by having larger leaves (50-160 × 20-60 mm) with attenuate-dentate margins.
Quercus wislizenii reportedly hybridizes with Q . agrifolia and Q . kelloggii (W. B. Brophy and D. R. Parnell 1974).