Plants 0.5--1.5 cm. Stem leaves curved, erect-appressed, slightly twisted and ± crisped when dry, linear-lanceolate, 1--2.2 mm, leaf base ovate, concave; margin plane, distal laminal cells 6--10 µm wide, with small, conic papillae, sometimes smooth; basal laminal cells elongate to elongate-elliptic, very thick-walled, not nodose. Sexual condition autoicous. Seta 1.5--4 mm. Capsule short-oblong to oblong-cylindric when old, 0.6--2.2 mm, lightly 8-ribbed 1/3--1/2 length; stomates numerous near middle; peristome double; endostome segments 8, incurved; exostome teeth 8, reflexed, papillose, often reticulate and perforate at apex. Calyptra conic, sparsely hairy. Spores 35--60 µm.

Branches and trunks of trees, coastal temperate rain forests; low elevations; B.C.; Alaska, Idaho, Oreg., Wash. Restricted to nw North America.

This species is distributed along the west coast from northern California, north to northern-most coastal British Columbia, and known inland only in northern Idaho. It is easily differentiated from other species by having creeping stems with many erect branches (much like a Macromitrium) and leaves with filiform apices. Also, the stomates are located at the middle of the capsule, not at the capsule base as in other species of the genus. The spores are large (greater than 35 µm). It is possible that the Japanese species, U. reptans, also occurs in North America; this species, resembling U. megalospora in growth form but with smaller spores and non-filiform leaf apices, should be looked for.