Deutsche Bot. Monatsschr. 22: 82. 1911
Plants large, erect, in loose to dense turfs or hummocks, golden to yellow-green or golden brown. Stems pinnate or subpinnate in one plane; hyalodermis absent, central strand present; paraphyllia absent; rhizoids many (sometimes reduced or absent), from proximal abaxial costa surface, forming conspicuous tomentum over one entire side of stem, strongly branched, smooth, sometimes warty-papillose at base; axillary hairs 2–5(–6)-celled, distal cells 1 or 2, hyaline. Stem leaves erect to erect-spreading, straight or falcate-secund, long-lanceolate to ovate-lanceolate, strongly plicate, (2–)2.5–4 mm; base not decurrent; margins plane or narrowly and tightly recurved, entire or sinuate, limbidia absent; apex slender- or long-acuminate; costa single, ending near apex; alar cells not or poorly differentiated; medial laminal cells long-linear to vermicular. Branch leaves similar, smaller. Sexual condition dioicous, often sterile. Capsule inclined to horizontal, oblong-cylindric, arcuate; peristome perfect; exostome teeth bordered; endostome cilia 2–3(–4), well developed, nodulose. Spores 12–18 µm.
North America, Europe, Asia, Atlantic Islands (Iceland).
Species 2 (2 in the flora).
The major characters for Tomentypnum are the erect habit, thick rhizoidal tomentum on one side of stem, presence of rhizoids on the proximal abaxial surface of the costa, strongly pluriplicate leaves, absence of clearly differentiated alar cells, and the presence of a stem central strand that can vary from sharply defined to barely discernible on the same stem. However, in arctic-alpine environments, plants of both species of Tomentypnum will be found without tomentum or with reduced tomentum; these plants were at times described as varieties of T. nitens but are now considered phenotypes of harsh environments. Contrariwise, plants with tomentum around the whole circumference of the stems are sometimes encountered. As pointed out by R. Gauthier (1987), some variability in the curvature of the leaves is occasionally present on some plants, but atypical leaves are usually localized to a few branches or to a sector of the stem. An invalid orthographical variant ("Tomenthypnum") is widely used in North America; the spelling retained here is the original used by Loeske. The habitat preferences of the two species, although quite distinct, do overlap to some extent as suggested by the existence of a number of intermixed populations, usually from moderately rich fen habitats (D. H. Vitt and C. D. Hamilton 1975; Gauthier).
|1||Leaves falcate-secund, often twisted distally, widest just beyond base; rhizoid initials restricted to stem leaf proximal costa surface; usually in Sphagnum-dominated vegetation.||Tomentypnum falcifolium|
|1||Leaves straight, not or little twisted distally, widest at base; rhizoids initials on stem leaf proximal abaxial costa surface and on stems just below leaf insertion; rich fens.||Tomentypnum nitens|