Stereodon plicatulus Lindberg
Plants small to medium-sized, soft, often regularly pinnate, pale yellow-green to golden green, procumbent to suberect, 2--5 cm, with branches 0.2--0.5 cm, leafy main stem 0.05--0.1 cm broad. Stems yellow green or green, occasionally with tinge of brown, hyalodermous, central strand weak or absent; pseudoparaphyllia foliose, often forked with attenuate tips to lobes. Leaves of stem curved to falcate-secund, 1--1.5 × 0.5--0.8 mm, ovate-lanceolate to narrowly triangular, curving to auriculate base and tapering to long-attenuate apex, margin plane, often toothed on auriculate portion, entire or toothed distally; costa short and double or obscure; leaf cells 50(--60)--70(--80) × 4--4.5 µm, basal cells shorter and broader, pitted alar cells 5--6, often colored, triangular to rectangular or rhomboidal, 6--15 µm long, thick walled except for the most distal one and outermost one, sometimes reduced or absent. Sexual condition dioicous (phyllodioicous). Seta red to red-brown, 2--2.3 cm. Capsules inclined, curved, cylindric, 1.5--2 mm excluding conic operculum, 0.7--0.8 mm wide, annulus 1--2-seriate; cilia of endostome 2, as long as segments. .
Sporophytes produced infrequently in summer, capsules maturing July--Aug. Common at tree bases and up tree trunk, also on logs, over humus on cliff shelves and rocks, also on forest floor, bog margins, and in tundra; 0--2000 m; Greenland; Alta., B.C., Man., N.B., Nfld., N.W.T., N.S., Nunavut, Ont., Que., Yukon; Alaska, Ga., Me., Mich., Minn., N.Y., N.C., Tenn., Wis.; Europe; Asia.
Hypnum plicatulum is a predominantly boreal to Arctic species, and is scattered in the Northern Hemisphere. This species is easy to recognize in most cases. The frequently close-pinnate, yellowish green to golden green plants with green to yellow stems, hyalodermous, auriculate leaves with a few differentiated cells that are sometimes excavated all provide useful features. See also discussions under Hypnum callichroum, H. hamulosum and H. holmenii.