1a2. Hygroamblystegium varium var. humile (P. Beauvois) Vanderpoorten & Hedenas, J. Bryol. 31: 131. 2009.
Hypnum humile P. Beauvois, Prodr. Aethéogam., 65. 1805; Leptodictyum humile (P. Beauvois) Ochyra
Stem leaves sometimes complanate, broadly ovate, 1.2-1.9 mm; margins entire or minutely serrate; apex acuminate; costa ending mid leaf to just below apex; alar cells not sharply differentiated, shorter than medial cells; medial laminal cells 30-60 × 9-15 µm, 3-7:1.
Wmeadows, fens, marshes; low to high elevations (0-3000 m); Alta., Man., N.B., Nfld. and Labr. (Nfld.), N.S., Ont., P.E.I., Que., Sask.; Ariz., Calif., Colo., Fla., Ga., Idaho, Ill., Ind., Iowa, Kans., Maine, Mass., Mich., Minn., Miss., Mo., Mont., Nebr., Nev., N.J., N.Mex., N.Y., N.C., N.Dak., Oreg., Pa., S.Dak., Tex., Utah, Vt., Wash., Wis., Wyo.; Mexico; Central America; South America; Europe; Asia.
Variety humile is easily recognized by a much shorter costa than has been associated with other names included within Hygroamblystegium varium, more elongate laminal cells, and undifferentiated alar cells. The length of the costa is, however, a plastic character that varies depending on water availability; in North America in particular, many specimens display a costa that ranges from ceasing at mid leaf to subpercurrent, rendering the distinction with other taxa within H. varium difficult. Variety humile often exhibits a complanate habit, which explains why the taxon has sometimes been associated with Leptodictyum, but this character also strongly varies, and molecular data unambiguously show that the taxon is nested within Hygroamblystegium. Variety humile also bears strong resemblance to Pseudocampylium radicale, from which it is distinguished by non-decurrent leaves.