Micromitrium synoicum is a leaf species described by Austin in Sullivant in 1874. Micromitrium synoicum is part of the genus Micromitrium and the Ephemeraceae family . Plants scattered or gregarious in persistent, but not usually abun-dant protonemata, pale green. Stems 0.2-3.7 mm. Leaves erect, lanceolate, often with a broad base, narrowly acuminate, 0.85-2 - 0.27-0.4 mm, margins usually - incurved beyond the middle, entire or nearly so. Sexual condition synoicous. Capsule dehiscing by a ring of differentiated cells at or distal to the equator, red-brown or red-black, globose or slightly flattened, slightly apiculate; exothecial cells in 1 layer, stomates none. Spores fewer than 100; various shapes, proximal face only rarely concave, 30-40 - 23-33 -m, dark red or dark brown.