Ephemerum Hampe, Flora. 20: 285. 1837.
Greek ephemeros, of short duration
Stems lacking. Leaves scarcely contorted when dry; costa well-developed, except generally lacking or weak in E. serratum; laminal cells lax in the proximal half of the leaf, in the distal half firmer, smaller, and usually papillose. Sexual condition dioicous or autoicous, commonly rhizautoicous. Capsule cleistocarpous, ovoid and distinctly apiculate, more than 0.5 mm from base to apex; exothecium of 2 cell layers; columella present in maturing capsules of E. cohaerens, but in other species visible only as pigmented areas at base and tip of the spore sac. Calyptra fugacious, cucullate, sometimes lobed or torn at the base, covering the distal 2/3 of the capsule, mostly more than 0.2 mm.
Species ca. 28 (4 in the flora): temperate and tropical regions nearly worldwide.
All Ephemerum taxa in the flora have the same chromosome number, n = 27. Mixed colonies are common, although hybrid forms are not evident. To a large extent, the species occupy similar ranges.