Aulacopilum Wilson, London J. Bot. 7: 90. 1848.
Plants small, forming thin mats, dull or glaucous olive green or brown. Stems creeping, irregularly pinnately branched, spreading complanate-foliate to subascending and terete; in cross-section outer 1-2 rows of cells rather small, thick-walled, inner cells large, thin-walled, central strand absent. Leaves appressed and weakly terete foliate when dry, loosely complanate when wet, ovate, to 0.6 mm long, mostly asymmetric, apex obtuse-rounded to bluntly acute or acute and ending in a hyaline apiculus or long piliferous tip; margins mostly plane, crenulate by projecting papillose cells; laminal cells hexagonal, pluripapillose over cell lumen, thin-walled, upper and median cells isodiametric; lower and occasionally marginal cells slightly elongate. Perichaetial leaves sheathing, slightly more elongate, to 0.8 mm long, apex acute to acuminate. Setae 0.7-1.2 mm long, smooth. Capsules exserted, urn short- to oblong-cylindrical to ovoid, 0.5-1.0 mm long; exothecial cells subquadrate, rather thick-walled; stomata absent or present in neck, superficial, opercula conic-apiculate; peristome absent. Calyptrae campanulate, enveloping capsule (to 1.6 mm long), usually persistent, moderately twisted (spiral), longitudinally plicate and opening by slits, surface smooth to lightly papillose. Spores finely papillose.