Orthoseira Guide
Credit: Marina Potapova and Sarah Spaulding
  1. Carinoportulae one to several, near midvalve
  2. Spines marginal, variable in length
  3. Frustules linked by spines to form short chains

The frustules of Orthoseira are cylindrical and form filamentous colonies linked by marginal spines. The valve surface is flat and possesses one or more unique process, the carinoportula. Internally, the valves may (or may not) have internal 'caverns', positioned at the valve mantle interface. The marginal spines, if present, are variable in length.

Orthoseira typically grows in subaerial habitats, often with bryophytes, in soils, and on the bark of tropical trees. The appearance of this genus in lakes and streams is considered incidental. Orthoseira is found from tropical to polar regions.