Ajo Mountain scrub oak

Quercus turbinella Greene subsp. ajoensis (C. H. Muller) Felger & C. H. Lowe; Q. turbinella var. ajoensis (C. H. Muller) Little

Shrubs, rarely trees , evergreen, to 2-3 m. Bark gray, scaly or furrowed. Twigs light brown, 1-2 mm diam., inconspicuously short stellate-pubescent or glabrate. Buds brown or reddish brown, ovoid or globose, 1-1.5 mm, variously short stellate-pubescent, tomentose, or glabrate. Leaves: petiole (2-)3-4 m. Leaf blade ovate to narrowly ovate or oblong, (10-)15-35(-50) × (5-)10-20(-30) mm, rather leathery, base cordate, rarely rounded, margins crispate, sometimes flat, cartilaginous, with 4-6(-8) long-attenuate, spinose-awned teeth on each side, secondary veins 5-8 on each side, whitish, apex acute or obtuse with bristly distal teeth; surfaces abaxially blue-green, waxy-glaucous, microscopically papillose, glabrous, sometimes sparsely stellate-pubescent along midrib, adaxially blue-green, glaucous, glabrous or sparingly stellate-pubescent along midrib, secondary veins raised on both surfaces. Acorns solitary or paired on thin axillary peduncle (5-)30-50 mm; cup shallowly cup-shaped, thin, 3-4 mm deep × 6-8(-10) mm wide, enclosing only base of nut, scales brownish, moderately tuberculate, pubescent; nut oblong to narrowly ovoid, 12-15 × 5-8 mm. Cotyledons distinct.

Flowering in spring. Rare to locally abundant on igneous slopes; 500-1500 m; Ariz.; Mexico (Baja California).

Populations of Quercus ajoensis in southern New Mexico show characteristics suggesting introgression from hybridization with Quercus toumeyi , such as increased twig and leaf pubescence and sometimes the prominent golden puberulum of the abaxial leaf surfaces. Hybrids between Q . ajoensis and both Q . turbinella and Q . gambelii (Utah) are also known.