Archidium Brid.

Elements in the following description are taken from Snider (1975).

Plants small, ephemeral or perennial, forming turves or tufts on moist soil in disturbed habitats. Stems erect, to 20 mm, simple or branched, often with sterile innovations in axils of the outer perichaetial or upper vegetative leaves; lower stems often becoming prostrate and stoloniferous and these giving rise to erect and fertile branches, which form rhizoids at base and often become detached; in cross-section with a central tissue of large, thin-walled cells, lacking a central strand, and the outer cells smaller and ± firmer-walled. Vegetative leaves triangular to linear-lanceolate, smaller but otherwise little differentiated from the perichaetial leaves.

Monoicous. Perichaetial leaves variable in shape but mostly ± lanceolate or triangular, entire or toothed; mid laminal and basal cells uniform throughout or becoming more quadrate at base and at lower margins; costa percurrent to strongly excurrent, in cross-section of uniformly thick-walled cells. Capsules globose, sessile, 1-several per plant, 200–750 µm diam., with 1 exothecial cell layer, releasing spores by irregular rupture or rotting of the capsule wall; setae not developed; stomata and columellae absent. Calyptra scarcely developed, consisting of an irregularly torn membrane attached to the remains of the vaginula. Spores usually few (4–176) per capsule, 1-celled, large (c. 50–300 µm) and thick-walled, maturing in spring or autumn.

A genus of nearly cosmopolitan distribution. Snider (1975) recognised 26 species in a worldwide monograph in which he proposed an infrageneric classification of two subgenera and several sections. One endemic species occurs in N.Z.