Trees , to 9 m; crowns open, narrowly rounded. Bark brownish gray, broken into narrow vertical scales or rather ragged strips. Twigs sparsely to moderately pubescent, often with stipitate glands. Leaves: petiole covered with stipitate glands. Leaf blade ovate or broadly ovate-elliptic to broadly elliptic or nearly orbiculate, 2.5--6.5 × 1.5--5 cm, base narrowly rounded to cordate or cuneate, margins sharply and unevenly doubly serrate, apex acute; surfaces abaxially pubescent, especially on veins. Inflorescences: staminate catkins 2--3 cm; pistillate catkins 0.6--1 cm. Infructescences 2.5--4 × 1.8--2.5 cm; bracts 1--1.8 × 0.5--1 cm. Flowering late spring. Streamsides and rocky slopes in moist canyons; 1200--2400 m; Ariz., N.Mex., Tex., Utah. Ostrya knowltonii occurs sporadically throughout the arid Southwest, including both rims of the Grand Canyon. On the basis of morphology and phytogeography, it appears to be more closely allied with Ostrya in mountainous western Mexico than with the eastern O . virginiana .

Plant: large shrub or small tree to 9 m tall, the trunks often several; bark grayish-tan; twigs moderately pubescent, becoming glabrous; hairs spreading, white; glands brown, long-stipitate to sessile Leaves: blades ovate-lanceolate (occasionally suborbicular or obovate), 0.7-6.0(-8.2) cm long, 0.7-5.2 cm wide, the bases rounded to obtuse and often slightly oblique, the apices usually acute to rounded, the margins sharply and irregularly doubly serrate; surfaces sparsely pubescent especially on the veins INFLORESCENCE: staminate catkins 1.5-3 cm long; pistillate catkins 0.7-1 cm long, in fruit to 4.5 cm long and about as wide, changing from green to white to tan, the bracts inflated, hop-like, 1-1.8 cm long, 0.5-1 cm wide Flowers: STAMINATE FLOWERS 3 per bract; stamens 3-6, the filaments divided, each part bearing an apically pilose anther sac. PISTILLATE FLOWERS 2 per bract Fruit: nutlets, ca. 6 mm long and 2 mm wide Misc: In moist canyons, usually near water; 1400-2150 m (4600-7000 ft.); late spring REFERENCES: Brasher, Jeffrey W. 2001. Betulaceae. J. Ariz. – Nev. Acad. Sci. Volume 33(1)