Achnanthidium Kranzii Guide
Credit: Marina Potapova
  1. Valves linear-lanceolate to linear-elliptic
  2. Striae radiate in the center, parallel at the ends
  3. Raphe valve with large rectangular central area
  4. Rapheless valve with elliptic or rhomboid central area
  5. Terminal raphe fissures curved to one side

Valves are linear-lanceolate to linear-elliptic with slightly drawn-out ends. The raphe valve has a large rectangular central area that often extends to valve margin. The rapheless valve has an apically elongated elliptic or rhomboid central area. Terminal raphe fissures are sharply curved to the same side. Striae are uniseriate, moderately radiate in the middle part of both valves, becoming parallel at the apices, 24-30 in 10 µm in the central valve, up to 40 in 10 µm at the apices.