Oaks of the World

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  Quercus potosina
Author Trel. 1924
Synonyms potosina f. exilis Trel. 1924
potosina f. aperta Trel. 1924
jaralensis Trel. 1924
Local names quebracho;  
Range Mexico (Durango, Zacatecas, San Luis Potosi, Jalisco, Chihuahua, Aguacalientes, Guanajuato); 180030500 m;
Growth habit 3-7 m tall, trunk to 15-30 cm in diameter; often forming 1-3 m tall thickets;
Leaves 3-8 cm long, 2-6 cm wide; evergreen; thick, subcoriaceous; oboval, elliptic, oboval-oblong or oblong-elliptic; apex obtuse to acute, with a mucronate tooth; base cordate auricled; margin thick, remotely revolute, cartilaginous, serrate-dentate with 2-8 pairs of mucronate teeth; dark green or yellowish green, lustrous above, with scattered, sessile, fascicled, stellate (a few) and long (to 0.2 mm) glandular hairs, glabrescent; beneath paler, with abundant trichomes identical to those of the adaxial face, covering the whole surface of the underside but leaving the epidermis visible; 7-9 vein pairs, straight, reddish and impressed above, prominent beneath ; epidermis glaucous, bullate and papillose ; petiole hairy, reddish, 2-5 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; 1-3 together or more; cup 0.8-1.2 cm in diameter, on a 1.6-2.5 cm long peduncle, with margin not rolled inside and pointed, woolly scales; enclosing 1/2 to 1/3 of nut; maturing in 1 year in September;

Bark, twigs and
buds

bark grey, scaly; twig rather thick (1.5-3 mm), reddish, pubescent; bud ovoid, acute, hairy, glabrescent, 3-4 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 ;
-- Section Quercus;
-- 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, and the abaxial face has a woolly, weakly yellowish tomentum.
Subspecies and
varieties
fo. aperta and fo. exilis Trel. 1924
Pictures