Quercus invaginata Trel.

Mexico (Coahuila, Chihuahua, Nuevo Leon, Tamaulipas); 1800-2000 m;

shrub often less than m;

2-5 x 1-3 cm; deciduous; leathery, rough; elliptic, oboval or oblong; apex obtuse or rounded, mucronate; base subcordate, seldom obtuse ; margin wavy, slightly revolute, with 2-7 pairs of mucronate teeth, seldom entire; dull green above, withe sparse stalkless fascicled hairs, glabrescent; paler beneath, with a dense tomentum made of sessile, fascicled, entangled hairs; 6-10 vein pairs, straight, weakly impressed above, prominent below; epidermis bullate; petiole tomentose, 2-4 mm long;

in May or June; male catkins 2-3 cm long, with numerous flowers; female inflorescences shorter, 0.5-1 cm, with 2-3 pubescent flowers;

acorn 1-1.5 cm long, 1 cm in diameter; ellipsoid; mucronate; grey at apex; solitary or 2-3 together on a very short peduncle; enclosed 1/3 to 1/2 by cup; cup turbinate, scaly, to 2 cm in diameter, with rim rolled inward (invaginate, hence the name); on the same tree one can find revolute acorn cup, and not revolute rim; maturing in 1 year in October;

withstands -16° C;

– A. Camus : n° 257; – Sub-genus Quercus, Section Quercus, Series Leucomexicanae;