Montana Field Guide

Morphological Category – Symmetric biraphid

Valves broadly lanceolate with rounded, rostrate apices. Raphe branches weakly lateral. Proximal raphe ends straight or deflected slightly to the secondary side. Distal raphe fissures hooked to the secondary side. Axial Area narrow and linear, widening slightly towards the central area. Central Area large, rounded and asymmetric, always smaller on the secondary side of the valve. Striae evenly spaced throughout, radiate in the center, becoming parallel to slightly convergent at the apices. Areolae 24–28 in 10 µm, visible in LM.

Size Range
Length 23-41 µm. Width 7.9-9.9 µm. Striae in 10 µm: 11-14.

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

Navicula elsoniana has narrower ends and grows in brackish water. Navicula hanseatica has more widely spaced striae and coarser areolae. Navicula rhynchocephala has longer valves and striae that are more widely spaced around the central area. Navicula rhynchotella is larger, has coarser areolae and grows in brackish waters.

Lakes, ponds and slow moving streams.

Cool, circumneutral to alkaline waters with low levels of nutrients and conductivity

Water Chemistry
pH range: 6.5-8.6
Conductivity range: 92-332 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.