Stephanodiscus Guide
  1. Striae radial and organized into fascicles
  2. Spines at valve face/mantle junction
  3. Valve face flat or concentrically undulate
  4. Marginal spines may be subtended by marginal fultoportulae
  5. Rimoportula(e) at level of spines

The valve face of Stephanodiscus species is flat or concentrically undulate. The striae are radial and organized into bundles, or fascicles. Fascicles are separated from one another by costae. Spines are present on the valve margin and a marginal fultoportula may be positioned below the spines. Internally, the areolae are covered by domed cribra.

Stephanodiscus is a diverse and widespread planktonic genus of freshwaters, primarily lentic (lake) habitats. Many species are variable in morphology (polymorphic) in response to the concentration of dissolved silica in the surrounding waters. Rapid speciation within the genus has been demonstrated based on sediment records in Yellowstone Lake, Wyoming.