Montana Field Guide

Morphological Category – Symmetric biraphid

Valves linear-lanceolate with triundulate margins and short rostrate-apiculate apices. Valves widest at the center. A Pseudoseptum present at each apex. Axial Area very narrow and linear, becoming wider near the central area. Central Stauros narrow and linear. Raphe filiform with straight and weakly inflated proximal ends. Striae parallel at the center to weakly radiate near the apices. Areolae very fine and difficult to resolve in LM.

Size Range
Length 13.9-15.3 µm. Width 3.8-4.8 µm. Striae in 10 µm 30.

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

Valves of Stauroneis smithii are longer than 20 µm and the smallest valves of S. smithii have a smooth rather than a triundulate outline.

Rivers and streams in the mountains (Bahls 2021).

Cool, alkaline waters with moderate nutrients and conductivity (Bahls 2021).

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.