5. Quercus viminea Trelease, Mem. Natl. Acad. Sci. 20: 123, plate 222. 1924.
Trees , evergreen or drought-deciduous, to 10 m. Twigs brown to dark reddish brown, 2-3 mm diam., sparsely to uniformly pubescent. Terminal buds brown to reddish brown, acutely ovoid, 1.5-2.5 mm, glabrous. Leaves: petiole 2-5 mm, pubescent. Leaf blade narrowly lanceolate, widest at or proximal to middle, 35-60[-150] × 7-10 mm, base usually rounded or obtuse, often oblique, occasionally somewhat cordate, margins entire with 1 apical awn, apex acute to acuminate; surfaces abaxially glabrous or with prominent tufts of tomentum near base of blade, adaxially glabrous or with pubescence along midrib and scattered on blade. Acorns (not known within our range) biennial; cup cup-shaped, 5-8 mm high × 8-10 mm wide, covering ca. 1/3 nut, inner surface pubescent, scales with appressed, obtuse tips; nut ovoid, 9-15 × 7-10 mm.
Flowering spring or summer. Habitat not specified; 1500 m; Ariz.; Mexico (Chihuahua, Sonora, and southward).
As with many of the Madrean counterparts of the oak flora, in very dry years trees progressively lose their leaves through the long dry spring and may become virtually leafless by the time the rains come in early summer (R. W. Spellenberg, pers. comm.).
In the flora, Quercus viminea is known from a single sterile specimen collected at Red Mountain, Santa Cruz County, Arizona. Recent attempts to find the taxon at this site have been fruitless. The Arizona specimen is similar to specimens from northern Mexico that have small, usually entire, narrowly lanceolate leaves with short petioles. These northern forms appear to grade clinally into larger-leaved southern forms that fit the general description of Q . bolanyosensis Trelease.