Montana Field Guide

Morphological Category – Symmetric biraphid

Valves lanceolate with short apiculate apices. Some valves have weak marginal undulations. Pseudoseptum present at each apex. Axial Area very narrow. Central stauros a transverse rectangle. Raphe filiform with straight and weakly inflated proximal ends. Striae weakly radiate throughout. Areolae closely spaced, about 30 in 10 µm.

Size Range
Length 21-37 µm. Width 5-6 µm. Striae in 10 µm 28-36.

Useful Link:
Diatom Glossary [Diatoms of North America website]

Our specimens differ from the type of this taxon in having weakly radiate rather than parallel striae. Stauroneis smithii var. incisa is distinguished from the nominate variety and from S. separanda by its smooth or weakly undulate margins. Stauroneis sagitta has more elliptic valves.

Lakes in the mountains.

Cold, circumneutral waters with low nutrients and conductivity.

Diatoms typically reproduce by cell division (mitosis) and occasionally by meiosis—sexual reproduction in which female and male gametes combine to form a specialized zygote called an auxospore. Repeated divisions result in cells of a population becoming progressively smaller and smaller. When cells reach a critically small size, sexual reproduction is initiated, resulting in an auxospore and initial cells that are the largest attainable for the species, after which cell division and size reduction resume (Amato 2010).

Climate change and regional warming.