1. Platydictya jungermannioides (Bridel) H. A. Crum, Michigan Bot. 3: 60. 1964.
Hypnum jungermannioides Bridel, Muscol. Recent., suppl. 2: 255. 1812; Amblystegiella sprucei (Spruce) Loeske
Plants dense, soft, silky, green to yellow-brown. Stems with branching angle narrow, branches easily detached; pseudo-paraphyllia absent; rhizoids axillary, purplish and granular-papillose at least when young. Leaves erect-spreading or sometimes ± secund, 0.1-0.3(-0.5) mm; base not or somewhat narrowed to insertion; margins serrulate, especially at insertion; alar cells subquadrate, region of 3-7 cells; distal laminal cells shortly oblong-rhomboid, 3-4:1. Specialized asexual reproduction by axillary obcuneate propagula. Sexual condition dioicous; perichaetial leaf margins ciliate-dentate distally. Seta 0.6-1.1 cm. Capsule erect, oblong- cylindric, symmetric or nearly so, 0.5-1 mm, contracted below mouth and at neck when dry, neck short; stomata in neck; annulus 2-seriate; operculum convex-conic, stoutly mammillate to ± rostellate; exostome teeth whitish yellow; endostome cilia 1 or 2, rudimentary to well developed. Spores 11-13 µm.
Rock in damp, sheltered places, crevices of cliffs, under rock ledges, peaty soil, humus under overhanging turf, hollows under roots of trees, lower sides of logs, calcareous habitats; low to high elevations; Greenland; Alta., B.C., N.B., Nfld. and Labr., N.W.T., N.S., Nunavut, Ont., Que., Sask., Yukon; Alaska, Ariz., Ark., Calif., Colo., Idaho, Iowa, Mich., Mont., N.Mex., N.Y., N.Dak., Vt., Wash., Wyo.; Europe; Asia.
Platydictya jungermannioides is easily recognized by its small size, absent or almost absent leaf costa, easily detached branches, and axillary rhizoids that are purplish and granular-papillose at least when young. The branching and rhizoid characters differentiate P. jungermannioides from the other three species of Platydictya.