Nearly worldwide in temperate and tropical regions.
Genera 2, species ca. 35 (2 genera, 8 species in the flora).
The Ephemeraceae are usually found in sunny or partly shaded areas, on moist or drying disturbed soil, where there is little competition from more persistent mosses and larger plants. They are visible for the most part as patches of greenish, alga-like protonemata with minute leafy plants and are best seen in the field when the protonemal mass is most abundant and green, with leafy plants that are green and approaching maturity.
The distinguishing characters of the leaves are derived from the largest, usually the most distal, leaves. The middle and proximal leaves vary in shape, marginal cells, and costal development. For example, the distal leaves bear the well-developed costa, but the proximal leaves are usually ecostate, and the middle leaves vary from ecostate to weakly or markedly costate. In the nominally ecostate species the proximal and middle leaves are ecostate, but the largest leaves, while in a strict sense ecostate, may have in the costal position thicker walled cells or a few undifferentiated cells in a double layer. As seen in cross-section, the double-layered cells are not organized as a costa and do not differ from other laminal cells, except that they may have very slightly thicker walls. In surface view the double layer is barely distinguishable.
|1||Calyptra minute, tightly adherent at or near the apex of the capsule, persistent; capsule cleistocarpous or with a ring of differentiated cells at or just distal to the equator, ± globose, without a well-developed, multicellular apiculus; costa commonly absent, but occasionally suggested by a few median cells with thick walls or in a short and indistinct double layer distal to the leaf middle; laminal cells lax, hyaline, smooth.||Micromitrium|
|1||Calyptra covering most of the distal half of the capsule, fugacious; capsule cleistocarpous, ovoid, and distinctly apiculate; costa well-developed, except mostly absent in Ephemerum serratum; laminal cells of the leaves lax in the proximal half and in the distal half firmer, smaller, and usually papillose.||Ephemerum|