Plants small to robust, not polytrichoid, in loose tufts. Stems simple or rarely sparingly branched. Leaves without a differentiated sheath, membranous, strongly crisped and contorted when dry, widely spreading and plane to ± distinctly concave when moist, with a differentiated border of 1 or more rows of narrow, linear, thick-walled cells, the border usually 2-stratose, the margins toothed to mid-leaf or below with single or paired teeth (teeth and cells of leaf border papillose in A. crispum); costa narrow, abaxially toothed in distal half or rarely smooth, bearing adaxial lamellae; abaxial lamellae none; lamina 1-stratose except for margins, often obliquely transversely undulate and abaxially toothed along the undulations, or almost plane and not abaxially toothed; lamellae ± straight or tall with sinuous margins, rarely rudimentary and almost absent, entire in profile, the marginal cells in section not differentiated, smooth; basal cells of lamina short-to long-rectangular, in longitudinal rows; median cells subquadrate to transversely elongate-hexagonal, in ± regular longitudinal rows, thin-to firm-walled, with or without distinct trigones, slightly convex on both surfaces (adaxial surface bulging-mammillose in A. angustatum), smooth or with minute rounded to striate papillae. Sexual condition dioicous, polygamous, or synoicous; perigonia inconspicuous, the bracts resembling the leaves, or the bracts broadly ovate and overlapping, forming a conspicuous disc, sometimes with more than one male inflorescence in sequence per plant; perichaetial leaves usually narrower and longer than the stem leaves. Seta 1(-3) per perichaetium, straight to flexuose, twisted near the capsule when dry, smooth. Capsule short-to long-cylindric, ± straight to arcuate, terete, finely striate when dry, absent a basal constriction; stomata none; exothecium smooth, the cells elongate-rectangular, not pitted, the longitudinal walls thickened; operculum rostrate, the beak straight to arcuate; peristome teeth 32, simple, linear and crowded. Calyptra cucullate, smooth or merely hispid at tip. Spores finely papillose, appearing smooth.
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