Hypnum minutissimum Sullivant & Lesquereux in A. Gray, Manual ed. 2, 678. 1856; Amblystegiella minutissima (Sullivant) Nichols; Platydictya jungermannioides var. minutissima (Sullivant) H. A. Crum

Plants thin, ± silky, green to brownish. Stems with branching angle wide, branches firmly attached; pseudoparaphyllia apparently absent; rhizoids below or at abaxial leaf insertion, red-brown, smooth. Leaves loosely spreading, 0.1-0.3 mm; base not narrowed to insertion; margins entire at insertion, serrulate elsewhere; alar cells scarcely differentiated; distal laminal cells elongate-rhomboidal, 3-6:1. Specialized asexual reproduction absent. Sexual condition autoicous; perichaetial leaf margins coarsely dentate distally. Seta0.4-0.9 cm. Capsule inclined, horizontal, or sometimes suberect, broadly oblong-ovoid, asymmetric, 0.4-0.5 mm, not contracted below mouth when dry, neck absent; stomata absent; annulus 1-seriate; operculum convex-conic, stoutly apiculate; exostome teeth yellowish; endostome cilia 1 or 2, well developed. Spores 8-13µm.

Moist, shaded rock (limestone, sandstone); low to moderate elevations; Que.; Ark., Ind., Mass., N.J., N.Y., Ohio, Pa., Wis.

Platydictya minutissima is rare and occurs in thin, rather silky mats. The leaves are somewhat remote, loosely spreading when dry, and serrulate except near the insertion; the laminal cells are elongate, and those in the alar regions are scarcely differentiated.