Ajo Mountain Scrub Oak

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.

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.

Ariz.; Mexico (Baja California).

Flowering in spring.

Rare to locally abundant on igneous slopes; 500-1500m.

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

Quercus ajoensis is an uncommon North American shrub with the common name Ajo Mountain shrub oak. It has been found in Arizona mountain ranges of the Colorado desert, and Arizona uplands of the Sonoran desert. Q. ajoensis integrates with Q. turbinella and is difficult to determine specimen identification due to hybridization. It appears that this species is an elevation variant of Q. turbinella and is best treated as a subspecies or variety as it has been treated in the past. The status of Q. ajoensis as a species is probably unnecessary due to complete integration with Q. turbinella or it being a low elevation variant of Q. turbinella.

Q. ajoensis is usually a shrub but occasionally attains the stature of small trees up to 3 metres (10 feet) tall. The leaves are narrowly egg-shaped, up to 5 centimetres (2 inches) long, with sharp pointed teeth.

The species is named for the Ajo Mountains in western Pima County, Arizona, southwest of the town of Ajo. The species does not occur as an identifiable species outside the Ajo mountain range and most specimens are of integrated types with Q. turbinella. The word "ajo" is Spanish for "garlic."