20. Hypnum revolutum (Mitten) Lindberg, Öfvers. Kongl. Vetensk.-Akad. Förh. 23: 542. 1867.
Stereodon revolutus Mitten, J. Proc. Linn. Soc., Bot., suppl.: 97. 1859
Plants small to medium-sized, rusty brownish to yellowish (occasionally dark green). Stems 2-5 cm, yellow-green, erect, suberect, or creeping, regularly to irregularly pinnate, branches0.2-0.7 cm; hyalodermis absent, central strand weakly developed; pseudoparaphyllia foliose, lanceolate to ovate. Stem leaves straight to falcate-secund, ovate or broadly ovate-oblong, gradually narrowed to apex, 0.5-1.8 × 0.4-0.6 mm; base not decurrent, not auriculate; margins revolute from base to near apex, entire at apex; apex narrowly acuminate; costa distinct to rarely ecostate; alar cells , region not well defined, , 8-15 cells in marginal row, forming clearly defined angles, 2 or 3 larger, hyaline, rectangular cells in decurrent portion; basal laminal cells wider than medial cells, sometimes yellowish, walls porose, pitted; medial cells 25-40 × 4-5µm, . Branch leaves similar, slightly smaller. Sexual condition dioicous; . Seta yellowish to reddish when mature, 1-2 cm. Capsule inclined to horizontal, dull yellowish to brown, oblong-cylindric, 2-3 mm; annulus 2 (or 3)-seriate; operculum conic; endostome cilia 2 or 3.
Varieties 2 (2 in the flora): North America, s South America, Europe, Asia, Antarctica.
Hypnum revolutum is circumpolar in the Northern Hemisphere but bipolar in distribution. The species occurs at sea level in the northern portion of its range but is most frequent at higher elevations. Strongly revolute leaf margins are found in the genus only in H. revolutum, and the areolation in combination with the alar cell differentiation usually make this species readily recognizable. Creeping plants tend to be pinnate, sometimes closely and regularly; suberect plants tend to be more loosely and irregularly branched. The longest branches are the ones most distant from the stem apex. Plants of H. revolutum have outer stem cell walls often thin and collapsed inward; the stem leaves are concave. The antheridial and archegonial plants are alike.