Flora 20: 285. 1837,.
Plants up to 2.5 mm, scattered in sparse protonemata. Leaves lanceolate, broadly linear or ligulate, acuminate, sometimes narrowed distally from shoulders, 0.8–2.5 × 0.15–0.4 mm; margins serrulate or serrate, with teeth sometimes recurved up to 45°; apex acuminate and papillose; costa at the base thin or not always apparent, stronger distally, often filling the acumen, percurrent or excurrent, papillose; areolation firm proximally and distally compact to dense; median laminal cells in ± vertical rows, smooth or slightly papillose; distal laminal cells papillose. Capsule with columella resorbed before meiosis; stomates in proximal half or scattered throughout. Spores various, 43–120 × 35–80 µm.
North America, Europe, e Asia, Pacific Islands (New Zealand).
Varieties 2 (2 in the flora).
|1||Distal leaves lanceolate to broadly linear and acuminate, with compact to rather dense areolation in the distal two-thirds||Ephemerum crassinervium var. crassinervium|
|1||Distal leaves broadly lanceolate to oblong-lanceolate or ligulate and subulate, often narrowed from a slight to prominent shoulder, densely papillose in the distal half||Ephemerum crassinervium var. texanum|