Plants: dense, green to brownish. Stems: with branching angle wide, branches firmly attached; pseudoparaphyllia foliose; rhizoids below or at abaxial leaf insertion, red-brown, smooth. Leaves: erect-spreading, often subsecund, 0.2–0.5 mm; base somewhat narrowed to insertion; margins entire or nearly so; alar cells subquadrate, region of 6–8+ cells; distal laminal cells oblong-rhomboid, (2–)3–5:1. : Specialized asexual reproduction absent. Sexual: condition autoicous; perichaetial leaf margins entire. Seta: 0.7–1.2 cm. Capsule: erect or nearly so, oblong-cylindric, symmetric, 1–1.5 mm, somewhat contracted at neck and sometimes below mouth when dry, neck short; stomata in neck; annulus 1-seriate; operculum conic, obliquely short-pointed to rostellate; exostome teeth yellow-brown; endostome cilia 1 or 2, rudimentary or absent. Spores: 9–13 µm.
Bark at base of hardwoods, exposed roots, logs. low to moderate elevations. N.B., Nfld. and Labr., N.S., Ont., P.E.I., Que., Yukon, Ariz., Ark., Ind., Maine, Mass., Mich., Mo., N.H., N.J., N.Y., N.C., Okla., Vt., Va., Wis., South America, Europe, Asia.
Distinctive features of Platydictya subtilis include the entire leaf margins, elongate distal cells, and many subquadrate alar cells; the capsule is erect or nearly so. This is the only species of the genus typically found on bark.