Montana Field Guide

Morphological Category – Symmetric biraphid

Valves broadly lanceolate with rounded apices. A prominent pseudoseptum is present at each apex. The Axial Area is broad, about three times the width of the Raphe, widening near the central area. Central Area a nearly rectangular stauros, expanding slightly near the valve margins. External raphe fissures lateral, becoming reverse lateral and strongly curved near the large, proximal pores. Striae radiate throughout and extend onto the valve mantles. Areolae round, coarse, 12-16 in 10 µm. Cells commonly joined, face-to-face in colonies.

Size Range
Length 122-182 µm. Width 26-33 µm. Striae in 10 µm 11-12.

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

In comparison to Stauroneis kishinena, S. americana has straight and unexpanded proximal raphe ends. Stauroneis finlandia and S. ursamaioris have protracted ends and more closely spaced striae.

Mountain pond in the forest.

Cool, circumneutral water 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).

Stauroneis kishinena is a cold-water stenothermal diatom that has been rated as being of high risk of extirpation in Montana due to climate change and regional warming (Bahls 2018).