Ephemerum Hampe, 1837.

Ephemerum is probably the smallest moss in California. Throughout low elevations in the state, it can be found from December to late March on eroded mineral soil and even on the trampled soil of paths and playgrounds. The plant will not be likely to be collected except with sporophytes; even then, hand-lens viewing often yields only a suspicion that it might be there. Ephemerum is best recognized in the field by the densely placed cushion of erect or matted protonemata resembling strands of a green alga. These protonemata may rise more than 1 mm off the soil surface, and they may therefore obscure the narrow, almost strap-shaped leaves. It may be appropriate here to mention that moss protonemata are separable from green algal filaments in that that the cross-walls in the filaments of a moss protonema are oblique to the long axis whereas they are transverse in a green alga.
see key to Acaulon Etc.

Species included:
Ephemerum serratum (Schrader ex Hedwig) Hampe