Oaks of the World

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  Quercus potosina

Trel. 1924 Mem. Natl. Acad. Sci. 20: 84

Diagnosis here

Synonyms potosina f. exilis Trel. 1924
potosina f. aperta Trel. 1924
jaralensis Trel. 1924 Diagnosis here
Local names quebracho;  
Range Mexico (Durango, Zacatecas, San Luis Potosi, Jalisco, Chihuahua, Aguacalientes, Guanajuato, Querétaro, Tamaulipas); 1800-3000 m;
Growth habit 3-7 m tall, trunk to 15-30 cm in diameter; often forming 1-3 m tall thickets;
Leaves 3-4.5 cm long, 1.4-2.3 cm wide; evergreen or lately deciduous; thick, coriaceous; oboval to elliptic; apex obtuse to acute, with a mucronate tooth; base subcordate auricled to rounded, sometimes asymmetrical; margin thick, remotely revolute or not at all, cartilaginous, serrate-dentate with 4-5 pairs of strongly mucronate teeth on the apical 3/4; dark green or yellowish green, lustrous above, with scattered, sessile, stellate hairs and long (to 0.2 mm) glandular ones, glabrescent; beneath paler, with sessil fascicled trichomes and abundant glandular trichomes covering the whole surface of the underside but leaving the epidermis visible; 4-7 vein pairs, straight, reddish and impressed above, prominent beneath ; epidermis glaucous, papillose ; petiole hairy, reddish, 3-7 mm long;
Flowers in April; male catkins 2-3 cm long, with numerous flowers; pistillate inflorescences less than 1-2 cm long, with 1-4 flowers scattered or clustered on a tomentose stalk 1-2 cm long;
Fruits acorn 1.2-1.5 cm long; ovoid; mucronate; 1-2 together or more; cup 0.8-1.2 cm in diameter, sessile , with margin not rolled inside and pointed, woolly scales; enclosing 1/2 of nut; maturing in 1 year in September to November;

Bark, twigs and

bark grey, scaly; twig rather thick (1.5-3 mm), reddish, pubescent; bud ovoid or globose, hairy, glabrescent, 3 mm long; stipules 6-10 mm long, pubescent, persistent around terminal bud.
Hardiness zone, habitat not quite hardy; prefers dry places;
Miscellaneous -- A. Camus : n° 254 ;
-- Sub-genus Quercus, Section Quercus, Series Leucomexicanae;
-- Resembles Q. repanda, but this species is much smaller (0.3-1.2 m), has the tomentum of the underside of the leaf that covers totally the epidermis, and the glandular trichomes adaxially are less than 0.05 mm long.
-- Possible confusion with Q. greggii, but this species has strongly coriaceous, stiff leaves, with markedly revolute margin with 2-3 veins pairs, and the abaxial face has a woolly, weakly yellowish tomentum.

Subspecies and
fo. aperta and fo. exilis Trel. 1924