Chisos hop-hornbeam, Big Bend hop-hornbeam

Ostrya knowltonii Coville subsp. chisosensis (Correll) E. Murray

Trees , to 12 m; crowns open, cylindric. Bark brownish gray, broken into narrow vertical strips. Twigs sparsely to moderately pubescent, without stipitate glands. Leaves: petiole glabrous or pubescent, without stipitate glands. Leaf blade broadly elliptic to elliptic-lanceolate, 3.5--5 × 2--3 cm, base narrowly rounded to cordate or cuneate, margins finely doubly serrate, apex obtuse to acute; surfaces abaxially sparsely pubescent, especially along veins. Inflorescences: staminate catkins 3--4 cm; pistillate catkins 0.8--1.5 cm. Infructescences 2--4 × 1.5--2.5 cm; bracts 1--1.8 × 0.5--1 cm.

Flowering late spring. Streamsides and moist slopes in canyons; of conservation concern; 1500--2300 m; Tex.

Ostrya chisosensis is endemic to Big Bend National Park, Texas. It appears to be related to O . knowltonii and to populations of hop-hornbeams in the mountains of western Mexico; the complex has not been studied in detail.