Plants 2--7 mm. Stem leaves loosely-erect when dry, ovate-lanceolate to oblong, 1.8--3 mm, gradually acute to a ± serrate, hyaline awn; margins revolute nearly to base of awn; distal laminal cells 14--24 µm wide, 1-stratose, smooth or with 1-2 small, conical papillae; basal laminal cells broadly rectangular, non nodose. Sexual condition autoicous. Seta less than 1 mm. Capsule immersed to emergent; urn oblong to oblong-cylindric, 1.2--1.8 mm, wrinkled or moderately 8-ribbed when dry; stomates immersed, numerous, at middle of capsule; peristome double; endostome segments 16, of 1 or 2 rows of cells, densely papillose; exostome teeth 16, reflexed when old and dry, longitudinally-striate or coarsely and densely papillose. Calyptra conic-oblong, naked or with a few, smooth hairs. Spores 13--20 µm.

Bases and trunks of trees less than 2 m, in dry, usually exposed areas, rarely on rock; 100--1000 m; B.C.; Alaska, Ariz., Ark., Calif., Colo., Kans., La., Mo., Neb., Ohio, Okla, N.Mex. S.Dak., Tenn., Texas, Utah; South America (Uruguay) ; Europe; n Asia; Africa (Algeria); Atlantic Islands (Canary Islands).

Orthotrichum diaphanum is distinguished by the hyaline awn of the distal stem leaves. Gametophytically, O. diaphanum is most closely related to O. pumilum, with which it shares the following attributes: large chlorophyllose leaf cells that lack large papillae, presence of numerous gemmae, and ovate-lanceolate leaves. Orthotrichum pumilum has apiculate leaf apices that often are similar to those found on the young plants of O. diaphanum.