Micromitrium megalosporum is a species of moss in the family Ephemeraceae . This species was first described in 1870 by Austin. Plants scattered or gregarious in usually sparse protonemata, yellow-green to orange-brown. Stems less than 0.2 mm. Leaves erect or spreading, broadly ovate-lanceolate and somewhat clasping at base, acuminate, 0.5-1.1 - 0.14-0.43 mm, margins usually - incurved beyond the middle, entire proximally and distally entire to serrulate. Sexual condition synoicous. Capsule cleistocarpous or rarely dehiscing by a ring of differentiated cells distal to the equator, orange-brown, globose or slightly flattened, rarely broadly ovoid, with a short, broad apiculus; exothecial cells in 2 layers, stomates confined to distal half, sometimes absent. Spores fewer than 100, various shapes, proximal face only rarely concave, 55-83 - 37-67 -m, orange-brown.