Montana Field Guide

Morphological Category – Symmetric biraphid

Valves narrowly lanceolate with subtly protracted and broadly rounded apices. Axial Area narrow and linear, widening somewhat towards the central area. Stauros a bit wider near the valve margins than at the center. One to three short striae usually present on each side of the central area. Raphe fissures lateral. Proximal ends nearly straight, tipped by very small pores. Raphe branches becomes filiform just short of the terminal fissures. Terminal Fissures hooked towards the secondary side. Striae radiate, becoming strongly radiate near the apices. Areolae fine, 18-22 in 10 µm.

Size Range
Length 93-137 µm. Width 14-20 µm. Striae in 10 µm 21-24.

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

Stauroneis beeskovea shares the same valve shape and strongly radiate striae as S. mangelsdorffii, from which it may be distinguished by its larger valves (>70-80 µm long) and finer, more closely spaced areolae (>12-14 in 10 µm). Stauroneis subborealis has a lower stria density, less radiate striae and proximal raphe ends that are curved rather than straight.

Mountain lakes and ponds.

Cold, circumneutral waters with very low nutrients and conductivity (Bahls 2021).

Water Chemistry
In Montana waters, pH ranges from 6.6 to 8.0 and specific conductance ranges from 10 to 67 µS/cm.

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.