Montana Field Guide

Morphological Category – Symmetric biraphid

Valves lanceolate with gradually attenuated, broadly rounded subrostrate apices. A shallow pseudoseptum occupies both apices. Axial Area narrow, about twice the width of the raphe, expanding somewhat near the stauros. Central Stauros transversely rectangular or weakly expanded towards the margins. Raphe lateral, becoming thread-like near the proximal and distal ends. Proximal raphe ends bent weakly to one side and tipped with small pores. Distal raphe fissures curved to one side. Striae radiate throughout. Areolae fine, 18-22 in 10 µm.

Size Range
Length 47-92 µm. Width 12-13 µm. Striae in 10 µm: 18-24.

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

Stauroneis clarkia is distinguished from S. hyperborea and S. subhyperborea by its wider apices, narrower axial area and more rectangular central area.
Stauroneis clarkia is much larger than S. lewisii and S. obtusa.

Seeps, springs and headwater streams in the mountains.

Cold, circumneutral waters with low 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.