Plants slender. Branch leaves 0.7--1.2 mm, acute to narrowly obtuse; cells papillose, up to 22 µm, margins of distal cells bulging. Perichaetial leaves longer. Seta 4--6.5 mm. Capsule 1.3--2 mm; exothecial cells not or slightly differentiated; peristome single, consisting of low, densely papillose membrane. Calyptra obscurely plicate, mitrate but many times splitting by single cleft along one rib. Spores 33--42 µm.

Dry mountain tops and slopes of the southern Blue Ridge escarpment, abundant, sometimes covering entire tree trunks of Pinus, Juniperus, and Quercus; 600 m and above; Ga., N.C., S.C., Tenn.; Mexico; West Indies; South America; Asia (China, Japan, Korea, Taiwan).

Macrocoma tenue subsp. sullivantii differs from other species in the Orthotrichaceae by having slender, creeping stems with erect branches. The leaves are erect-appressed, and the basal cells of the leaves are rounded-quadrate. It is very closely related to a Mexican species, M. orthotrichoides, which differs in having a peristome and its sparsely hairy calyptra. Macrocoma tenue subsp. tenue is Old World in distribution.