Plants: very small, light to dark green or brownish. Stems: freely and irregularly branched; hyalodermis absent, central strand narrow or absent; paraphyllia absent; rhizoids or rhizoid initials below or at abaxial leaf insertion, or axillary, rarely forming tomentum, slightly branched, smooth or granular-papillose; axillary hair distal cells 1 or 2, hyaline. Stem: leaves erect-appressed to loosely spreading, sometimes subsecund, lanceolate, not plicate, very small, 0.1–0.3(–0.5) mm; base not decurrent; margins plane, entire to serrulate, limbidia absent; apex acuminate, acumen plane; ecostate or costa double, very short, indistinct; alar cells scarcely differentiated to subquadrate, region small, inconspicuous, along basal margins; medial laminal cells subquadrate, oblong-rhombic, or short-rhomboidal; marginal cells 1-stratose. Sexual: condition autoicous or dioicous. Capsule: erect or variously inclined, oblong-cylindric to oblong-obovoid, symmetric or asymmetric; peristome perfect or somewhat specialized; exostome margins entire or dentate distally; endostome cilia absent or 1–3, rudimentary to well developed. Spores: 8–13 µm. North America, South America, Europe, Asia.
Species 10 (4 in the flora). Platydictya resembles Amblystegium but is smaller and has virtually ecostate leaves. The capsule is variously inclined and asymmetric but not slender-cylindric, curved-asymmetric, or greatly contracted below the mouth and at the neck when dry. The genus is placed in Amblystegiaceae despite its ecostate, often secund leaves that suggest an alliance with Hypnaceae. The treatment by L. S. Cheney (1897) of Amblystegium, in a broad sense, is a useful reference for the species of Platydictya. Plants of Platydictya have creeping stems, slightly concave leaves, and finely papillose spores.