Mohr oak

Shrubs or trees , evergreen or deciduous, shrubs erect, rhizomatous, trees small, 0.5-3 m. Bark pale, rough and deeply furrowed. Twigs yellowish or whitish, 1-2 mm diam., felty-tomentose. Buds dark red-brown, round-ovoid, 2 mm, glabrous, occasionally puberulent on outer scales, not subtended by persistent, hairy, subulate stipules. Leaves: petiole 2-5 mm. Leaf blade usually strongly bicolored, oblong or elliptic, (15-)30-50(-80) × (10-)20-30(-35) mm, leathery, base rounded, rarely cuneate or cordulate, margins entire or toothed or denticulate, undulate or flat, secondary veins 8-9 on each side, apex rounded or acute; surfaces abaxially densely gray- or white-tomentose with semi-erect curly, stellate hairs, secondary veins rather prominently raised, adaxially dark or dull green, lustrous or somewhat glaucous, with minute, scattered, semi-erect or appressed-stellate, (4-)6 or many rayed hairs, not felty to touch, secondary veins slightly raised or prominent within depressions. Acorns solitary or paired, subsessile or peduncle sometimes 10-15 mm, tomentose like twigs; cup shallowly to very deeply cup-shaped, 5-12 mm deep × 8-18 mm wide, enclosing 1/2 nut, base rounded or flat, margin thin, scales triangular-ovate to oblong, proximal scales coarsely tuberculate and canescent-tomentose, distal ones usually elongate and narrowed, tips appressed, reddish, thin, nearly glabrous; nut light brown, ellipsoid to ovoid, 8-15 × 5-12 mm. Cotyledons connate.

Flowering spring. Limestone hills and slopes, calcareous substrates; 600-2500 m; N.Mex., Okla., Tex.; Mexico (Coahuila).

Putative hybrids between Quercus mohriana Buckley and Q . grisea Liebmann are problematic and highly polymorphic. They are restricted to zones of contact between limestone, the preferred habitat of Q . mohriana , and igneous substrates, the preferred habitat of Q . grisea , or sometimes on dolomite, in western Texas.