Simonsenia Guide
Credit: Carrie Graeff
  1. Raphe within a raised canal
  2. Raphe positioned on valve margin
  3. Valve with regularly spaced depressions near margin

Simonsenia is a genus that possesses characters seen in both the Surirellaceae and the Nitzschiaceae. Its valve symmetry and general shape, with the raphe being present on only one valve margin, resembles that of many Nitzschia species. Also, the cribra of the areolae are similar to those in many Nitzschia species. However, its raphe is present in a canal that is raised above the valve surface, as in some species of Surirella and Stenopterobia. Prominent depressions in the valve surface underneath the raised raphe canal can resemble fibulae seen in Nitzschia, but the two structures are morphologically distinct; fibulae are entirely absent in Simonsenia.

In the United States, populations of Simonsenia are widespread in freshwater systems and can be indicators of high nutrient loads. In addition, at least one species of Simonsenia can be found associated with systems that experience relatively high variation in osmotic pressure.