Acrocarpous or pleurocarpous. Plants minute to large; stems simple to much branched, with or without central strand. Leaves spirally arranged, rarely distichous; costa single or double, well developed or not, or lacking; cells usually unistratose except sometimes at margins or towards apex, isodiametric to linear, thin-walled to strongly incrassate, smooth, papillose or mamillose. Early divisions of zygote resulting in radially symmetrical embryo. Setae short or long; capsules erect to pendulous, globose to cylindrical, dehiscing by lid or more rarely cleistocarpous; mouth with peristome of one (haplolepideous mosses) or two (diplolepideous mosses) concentric rings of articulated teeth, each ring of 16 simple or variously divided teeth, teeth variously ornamented, sometimes reduced or absent; spore sac cylindrical, surrounding but not overtopping columella; spores usually small, to 40 μm, numerous, mostly 5000–50 000 000 per capsule, usually wind-dispersed.
The nature of the peristome has been regarded as highly important in the classification of mosses. For accounts of the structure and ontogeny of peristome teeth see S. R. Edwards in Clarke & Duckett (1979) and S. R. Edwards in Schuster (1983).
Subclass 1 Diphysciideae
Dioicous or autoicous. Acrocarpous. Protonemata persistent. Stems short, simple. Leaves lingulate or lingulate-spathulate; costa present; cells unistratose at base, 2(−3)-stratose above, rounded-quadrate, mamillose or smooth. Perichaetial leaves larger than stem leaves; margins ciliate above; costa longly excurrent. Setae very short; capsules oblique, ovoid, gibbous, terete, tapering to small mouth; lid conical; outer peristome of 16 very short teeth, inner conical with 16 plicae. One family, genera.