Micromitrium Austin

Plants minute, mostly with sparse protonema, scattered or gregarious. Stems extremely short. Leaves erect, the lower lanceolate-acuminate, the upper narrowly lanceolate and long acuminate, entire or weakly and bluntly serrulate above; laminal cells thin-walled, rectangular below, in upper leaf hexagonal-rhombic. Costa absent or rarely present.

Synoicous, autoicous or rarely dioicous. Setae lacking; capsules sessile, globose, lacking an apiculus, lacking neck, dehiscing near the middle by a row of weakly differentiated cells; columella resorbed at maturity; exothecial cells thin-walled and laxly hexagonal; stomata, annulus, and peristome lacking. Calyptra minute and delicate. Spores medium-sized to large, mostly reniform.

Closely allied to Ephemerum from which it is distinguished by capsules that lack apical projections and have a minute, persistent calyptra (consisting of the remains of the archegonium). The majority, perhaps all species, lack stomata and nearly all have ecostate leaves. A genus of c. 10 species, mostly distributed in North and South America; one species occurs in N.Z. Most of the species in the genus were previously treated in the genus Nanomitrium Lindb.