Sonoran scrub oak

Quercus dumosa Nuttall var. turbinella (Greene) Jepson; Q. subturbinella Trelease

Shrubs or small trees , evergreen or subevergreen, to 4 m. Bark light gray or brown, scaly. Twigs brown to gray, 1-3 mm diam., usually tomentulose, sometimes glabrous, becoming glabrate. Buds brown, round to ovoid, 1-2 mm, minutely pubescent. Leaves: petiole 1-4 mm. Leaf blade elliptic or ovate, (1.5-)20-30 × (5-)10-15(-20) mm, thick, leathery, base cordate or rounded, margins planar or slightly crisped-undulate, coarsely 3-5-toothed or very shallowly lobed on each side, teeth spinose with spines 1-1.5 mm, secondary veins 4-8 on each side, apex acute or obtuse; surfaces abaxially yellow or reddish, usually glaucous, minutely stellate-puberulent, adaxially grayish, glaucous, or yellowish glandular, glabrous or sparsely and minutely stellate-pubescent. Acorns solitary or several, on axillary peduncle 10-40 mm; cup hemispheric or shallowly cup-shaped, 4-6 mm deep × 8-12 mm wide, covering 1/4-1/2 nut, scales tightly appressed, ovate, moderately tuberculate, grayish or yellowish puberulent; nut light brown, ovoid, to 20 × 11 mm, minutely puberulent or glabrate. Cotyledons distinct.

Flowering spring. Dry desert slopes, often in juniper and pinyon woodlands; 800-2000 m; Ariz., Calif., Colo., N.Mex., Nev., Tex., Utah; Mexico (Baja California, Sonora, and probably n Chihuahua).

Formerly, California populations of what here is referred to as Quercus john-tuckeri have been included in the concept of Q . turbinella . Quercus john-tuckeri has subsessile fruit and noncordate leaf bases as opposed to the consistently pedunculate fruit and strongly cordate leaf bases of Q . turbinella . The two species seem to be no more closely related to each other than each might be to other southwestern oaks, and Q . john-tuckeri shares at least as many characteristics with Q . berberidifolia as with Q . turbinella . Thus, treatment of these two taxa as varieties of the same species is inappropriate.

Quercus turbinella forms putative hybrid swarms with Q . gambelii (see treatment), as well as with Q . grisea .

SELECTED REFERENCES

Tucker, J. M. 1961b. Studies in the Quercus undulata complex. II. The contribution of Q. turbinella. Amer. J. Bot. 48: 329-339.