Gomphonema Sphaerophorum Guide
Credit: Ian Bishop
  1. Narrow, distinctly capitate headpole
  2. Single, isolated stigma present
  3. Striae parallel to weakly radiate
  4. Areolae punctate

Valves are clavate, with a distinctly capitate headpole and a narrow footpole. A stigma is present opposite a single shortened stria. Striae are nearly parallel mid-valve, becoming radiate at the apices. Areolae are distinctly punctate and visible in LM, measuring 25-27 in 10 ┬Ám.