Achnanthidium exiguum is easily distinguished from other monoraphid diatoms by the linear-elliptical valves with narrowly capitate to subrostrate apices and by the presence of a fascia on the raphe valve. Achnanthidium exiguum var. constrictum differs from the nominate variety only by strongly constricted valve margins. Smaller specimens of A. exiguum are sometimes incorrectly identified as Achnanthes exigua var. elliptica, because of their elliptic-lanceolate shape. Larger specimens of Achnanthes exigua var. elliptica, however, are needed to distinguish this variety from the nominate variety.

LM scalebar = 10 µm
Gs027521 28 Gs027521 15 Gs027521 21 Gs027521 6 Gs027521 18B Gs027521 26 Gs027521 24
Length Range
5-17 µm
Width Range
4.5-6.2 µm
Striae in 10 µm
24-34 in center of raphe valve, 20-25 in center of rapheless valve, up to 45 at apices

Also compare to

Achnanthidium exiguum var. constrictum

(Grunow) Andresen, Stoermer and Kreis

Achnanthes exigua var. elliptica