Montana Field Guide

Morphological Category – Symmetric biraphid

Valves elliptic-lanceolate to rhombic-lanceolate with triundulate margins and short apiculate apices. 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 weakly radiate throughout. Areolae closely spaced, 26-30 in 10 µm.

Size Range
Length 18-28 µm. Width 5.8-7.7 µm. Striae in 10 µm 25-30.

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

Stauroneis smithii is one of the most widespread and easily identified species of Stauroneis in the United States.

Compared to Stauroneis smithii, Stauroneis separanda has smaller valves with more prominent apices. Unlike small valves of Stauroneis smithii, which have smooth margins, small valves of Stauroneis separanda have triundulate margins. Valves of Stauroneis smithii var. incisa have a higher stria density and are larger and less undulate.

Mainly rivers and streams; also lakes, ponds and wetlands (Bahls 2021).

As an ecological generalist, Stauroneis smithii is widely distributed in a variety of habitats under varied water quality conditions (Bahls 2021). It is seldom found in abundance.

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 (Amato 2010). 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.

None are apparent (Bahls 1968-Present; Bahls 2021).