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Guide to Pinnularia formica

(Ehrenb.) R.M.Patrick 1966

Pinnularia Formica Guide
  1. Central expansion distinct
  2. Apices capitate
  3. Striae constrained to valve margin

Valves are large. They have a distinct, longitudinally elliptic central expansion. Apices are expanded and capitate. The striae are constrained to the valve margin, so that the axial area covers most of the valve.