Leafl. Western Bot. 6: 20. 1950. Bryum obtusifolium Brid., Musc. Rec. 2: 52. 1803.
Pohlia cucullata (Schwaegr.) Lindb., Musci Scand. 19. 1879. -- Bryum cucullatum Schwaegr., Spec. Musc. Suppl. 1: 94. 68 1816.
Webera microcaulon C. Will. & Kindb. in Mac., Cat. Canad. Pl. 6: 114. 1892.
Webera polymorphoides Kindb. in Mac., Cat. Canad. Pl. 6: 111. 1892.
Plants erect in green to brownish green wefts, to 2.5 cm high. Leaves keeled along costa and appearing almost cucullate, ovate lanceolate to lanceolate with obtuse apices, to 1.5 mm long, about 2.5–3.5: 1, erect to imbricate when moist, little changed upon drying, not plicate. Median laminal cells elongate-hexagonal with thin walls (lumen: wall ratio 6–10: 1) 4–7: 1, smooth or distally prorate, not pitted, to 18 µm wide. Basal and alar cells shorter and and slightly broader than median cells. Cells near apex short elliptic 2–3: 1, typically somewhat distally prorate with these prorate cells also covering the distal portion of the costa. Margins not decurrent, plane above but often with some basal recurvature, minutely serrulate with right-angled teeth. Limbidium not clearly demarcated, unistratose throughout. Costa red-brown throughout, ending in the blunt leaf apex. Costa cross-section almost homogeneous but with scattered substereid cells. Axillary hairs 3–4 cells long, to 60 µm, with 1–3 basal brown cells and a much inflated and thin-walled terminal cell. Rhizoids to 12 µm wide at insertion, papillose, brown, sparingly branched, surrounding an isodiametric macronematal area to 60 µm wide. Stem cross-section round, with a well-defined central strand, with the hyaline and leptodermous inner corticals abruptly transitting to a single layer of only moderately pachydermous, red brown outer cortical cells, without a hyaloderm. Gemmae absent.
Paroicous with perigonia placed very near the perichaetia. Perichaetial leaves larger than vegetative leaves, to 3 mm long with bracts broadly elliptic and deeply keeled along costa, 2.5–3: 1, remotely serrulate with blunt teeth and with the cells near the leaf apex somewhat prorate. Seta lustreless dark-brown to almost black, smooth, erect but geniculate distally, to 15 mm long. Urn to 1.5 mm long, short-cylindric, 2–2.5: 1, inclined to pendent, neither sulcate nor strumose. Operculum short conic to almost dome-shaped. Annulus of 2–3 rows of inflated and thin-walled cells. Exothecial cells at capsule mouth to 12 µm broad, transversely elongate in one or two rows. Exothecial cells at middle of urn quadrate to rectangular, 1–2: 1, to 40 µm broad, in regular rows, evenly thick walled with lumen: wall ratio 4–8: 1. Stomates phaneroporous, restricted to neck of capsule, raised on short pustules, somewhat longer than broad. Exostome yellow-brown, to 250 µm long, inconspicuously shouldered, very inconspicuously horizontally striate with dorsal lamellae low. Endostome with basal membrane constituting less than 1/3 of total length. Segments smooth, about as long as exostome, broadly perforated along center line but almost not keeled. Cilia absent or almost so. Calyptra cucullate, mostly shed before capsule maturity. Spores to 25 µm, coarsely papillose.