Stems 1--6(--10) cm, matted with brownish rhizoids, often defoliate proximally, branches 1--2 cm, ascending and usually simple; paraphyllia becoming scarce in emergent plants. Stem leaves somewhat contorted when dry, 0.5--1.3(--1.5) mm; limbidia of 2(4) layers of cells, sometimes inconspicuous or disappearing before acumen or base, sometimes with spurs extending into the lamina; costa 40--60(--75) µm wide at base; distal laminal cells 6--12 x 15--20(--40) µm; basal cells with thick walls, sometimes pitted. Branch leaves similar to stem leaves, but slightly smaller and narrower. Perichaetial leaves 0.5--0.8 mm. Seta yellow to reddish brown, 10--30 mm. Capsule reddish-brown, 1.5--3 mm; exostome teeth yellowish-brown, cross-striolate proximally, papillose distally, trabeculate at back; endostome pale yellow, papillose. Calyptra yellow. Spores 12--17(--25) µm, yellowish-brown.

Capsules mature spring--early summer. Wet rocks, tree roots, rotting wood and bases of trees along streams, waterfalls and in seeps, submerged or in splash zone, in both lowland and montane deciduous or mixed deciduous-coniferous forest, both acid and calcareous rocks, widespread but often rare, sometimes locally abundant; 0--1500 m.; Ont., N.B., Nfld., N.S., Que., Ala., Ark., Conn., Del., Fla., Ga., Ill., Ind., Ky., La., Maine, Md., Mass., Mo., N.H., N.J., N.Y., N.C., Okla., Pa., S.C., Tenn., Tex., Vt., Va., W.Va (distribution after R. Ochyra 1987, supplemented by J. A. Christy).

The mostly bistratose margins, filiform paraphyllia, and saxicolous substrate in streams and seeps distinguish this taxon. It bears superficial resemblance to Amblystegium varium, Donrichardsia macroneuron, Hygroamblystegium noterophilum, Hygroamblystegium tenax and Platyhypnidium riparioides, but none of these have the limbidia characteristic of Platylomella. Sciaromium laxirete Abramova & I. I. Abramov, listed provisionally by R. Ochyra (1987) as a synonym of Platylomella lescurii, is known only as a Pliocene fossil from Bashkiria, western Eurasia.