Diadesmis Guide
Credit: Eugene Stoermer
  1. Areolae elongate
  2. Frustules small, usually less than 20 µm in length
  3. Cells form band-like colonies

Diadesmis is biraphid, although the raphe often becomes secondarily filled with silica. Frustules of Diadesmis are small, usually less than 20 µm in length. The striae are composed of areolae elongated in the transapical direction, a characteristic that may be difficult to discern in the LM. Frustules form band-like colonies, which may be linked by marginal spines. The raphe of some valves may be secondarily filled with silica, so that the raphe may not be evident. In girdle view, however, the central nodule and helictoglossa may be seen - evidence of the presence of a raphe.

Diadesmis is considered an aerophilic taxon. It grows on mosses and on damp rocks, often in low conductivity, slightly acid waters. With the description of the new genus Humidophila, Diadesmis now includes D. confervacea and varieties.