Quercus undata Trel.

Mexico, in the Sierra Madre Occidental (Chihuahua, Durango); 2000 - 2800 m ;

shrub, no more than 3-4 metres tall;

3-6 cm x 1-4; thick, leathery; elliptic; apex acute more or less broadly, seldom obtuse or rounded, mucronate; base obuse, rounded or cordate; margin entire or slightly dentate near apex, crispate, more or less revolute; adaxially greyish green, more or less densely tomentose; abaxially glaucous green, densely tomentose (sometimes moderately) with variable stellate trichomes; midrib with a yellow pubescence; 10-12 vein pairs impressed above; petiole 2-6 mm, thin, stellate tomentose;

male catkins 3 cm, woolly; loosy flowered, with anther glabrous and round.

acorn 1 cm in diameter, ellipsoid, 2-3 on a 6-10 cm long peduncle;

– Sub-genus Quercus, Section Quercus, Series Leucomexicanae; – The morphological characters are between those of the parents; however Q. x undata is closer to Q.chihuahuensis , but the trichomes of the abaxial surface of the leaves are stellate, as those of Q. grisea and Q. arizonica (they are stipitate fascicled in Q. chihuahuensis );