Montana Field Guide

Morphological Category – Symmetric biraphid

Valves lanceolate and very large with blunt, broadly rounded apices. Axial Area moderately broad and linear. Central Area a rectangular stauros, often narrowing somewhat towards valve margins. Shortened striae may be present in central area. External raphe fissures lateral. Proximal raphe ends straight and somewhat inflated. Striae radiate throughout. Areolae coarse, 11-14 in 10 µm.

Size Range
Length 215-386 µm. Width 38-60 µm. Striae in 10 µm 12-14.

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

The largest Stauroneis species in Montana is Stauroneis rex, and striking for its size (Bahls personal communication).

Stauroneis phoenicenteron has smaller valves than S. rex (26-35 µm wide by 129-199 µm long) and a higher stria density (15-18 in 10 µm). It is likely that S. rex has been misidentified as S. phoenicenteron in U.S. surveys.

Lakes and ponds, mainly in the mountains (Bahls 2021).

Warm, 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.