Oefv. K. Svensk. Vet. Akad. Foerh. 23: 542. 1867. -- Stereodon revolutus Mitt., J. Linn. Soc. Bot. Suppl. 1: 97. 1859.
Hypnum watsoni Lesq. & James, Proc. Amer. Acad. Arts Sci. 14: 138. 1879.
Plants in dense mats, green to almost golden green, irregularly but rather densely branched with branches and stems little different. Leafy axes similar wet or dry, to 5 cm long. Leaves to 2.5 mm, 3–4: 1, falcate secund to almost circinate, lanceolate to ovate-lanceolate, gradually contracted from the non-auriculate base to the very long acumen. Margins plane, narrowly decurrent, serrate near apex. Median cells smooth, 4–7 µm wide, linear, up to 20: 1, thin walled, not pitted. Two or three cells of extreme alar region inflated and isodiametric, to 20 µm wide, accompanied by up to 6 quadrate but not inflated supra-alar cells with moderately thick but unpitted walls. Costa inconspicuous, short and double. Pseudoparaphyllia deltoid to orbicular, strongly overarching the bud. Axillary hairs 5-celled, to 250 µm with a very long basal brown cell, not offset from leaf insertion. Stem cross-section without a central strand, with a hyaloderm markedly enlarged and thin walled compared to the adjacent several layers of small and brownish pachydermous cells, and with inner cortical cells enlarged with thin and hyaline walls.
Dioicous with male plants similar to females. Perichaetia in leaf axils, much shorter than the subtending leaves. Seta to 2.5 cm long, erect, pale yellow to yelloww. Capsule light brown, inclined to almost erect, arcuate, often strongly so, neither sulcate nor strangulate. Urn to 3 mm, about 3–4: 1. Exothecial cells near mouth of capsule isodiametric with thick walls and rounded lumens, to 15 µm wide. Exothecial cells at mid urn short rectangular, 1.5–3: 1, in regular rows, not collenchymatous, to 22 µm broad. Stomata phaneroporous, restricted to neck. Annulus present, not revoluble. Operculum conic, much shorter than urn. Exostome to 300 µm long, horizontally striate below, papillose above, light-brown. Endostome segments smooth to lightly papillose, perforate, about as long as exostome with basal membrane about 1/2 of total length. Cilia 2–3, nodose. Spores smooth to very lightly papillose, to 15 µm.