Encyonopsis montana

L.L.Bahls 2013      Category: Asymmetrical biraphid

REPORTED AS: Encyonopsis cesatiformis (Krammer 1997, plate 186, fig. 1, p. 422) | Encyonopsis cesati var. geitleri (Bahls 2012, Diatoms of the US) 

Encyonopsis microcephala


Encyonopsis neerlandica

LM scalebar = 10 µm = 80 pixels.


Contributor: Loren Bahls - May 2013
Length Range: 37-75 µm
Width Range: 7.0-8.8 µm
Striae in 10 µm: 19-21 at the valve center, 21-22 near the apices


Valves are rhombic-lanceolate and nearly symmetric with respect to the apical axis. Apices are rostrate and deflected slightly to the ventral side. The axial area is narrow. The central area is small, slightly asymmetric, and rounded on both sides. The raphe is lateral. Proximal raphe ends are deflected toward the dorsal side and distal raphe ends are hooked toward the ventral side. Striae are radiate throughout, more strongly radiate near the apices. Areolae are very fine and difficult to resolve in LM.

Note that figures 89 and 90 in the original description (below) are of Encyonopsis cesatiformis, not E. montana.

Original Description

Author: L.L.Bahls 2013
Length Range: 26-75 µm
Width Range: 5.7-8.8 µm
Striae in 10 µm: 18-22

Original Description

Valves broadly lanceolate in smaller specimens to rhombic-lanceolate in larger specimens, with short rostrate apices deflected ventrally. Valves not or slightly dorsiventral. Valve length 26–75 µm; valve width 5.7–8.8 µm. Axial area narrow. Central area small, asymmetric, rounded on the dorsal side, rounded (large specimens) to irregularly notched (small specimens) on the ventral side. Raphe lateral, becoming filiform near proximal and distal ends. Proximal raphe ends weakly expanded, deflected dorsally. Distal raphe fissures comma-shaped, curved toward the ventral side. Striae weakly radiate (center) to strongly radiate (ends), 18–22 in 10 µm.

Original Images

Cite This Page:
Bahls, L. (2013). Encyonopsis montana. In Diatoms of the United States. Retrieved April 22, 2018, from http://westerndiatoms.colorado.edu/taxa/species/Encyonopsis_montana

Species: Encyonopsis montana

Contributor: Loren Bahls

Reviewer: Rex Lowe


Bahls, L. (2013). Encyonopsis from western North America: 31 species from Alberta, Idaho, Montana, Oregon, South Dakota, and Washington, including 17 species described as new. Northwest Diatoms, Volume 5. The Montana Diatom Collection, Helena, 46 pp.

Krammer, K. (1997). Die cymbelloiden Diatomeen. Eine Monographie der weltweit bekannten Taxa. Teil 2. Encyonema part., Encyonopsis and Cymbellopsis. Bibliotheca Diatomologica 37:1-469.

Links & ID's

Index Nominum Algarum (INA)

Original INA

California Academy of Sciences (CAS)

North American Diatom Ecological Database (NADED)


Autecology Discussion

Encyonopsis montana is widely distributed and locally abundant in lakes in the Northern Rockies and North Cascades. For collection sites with water quality data, pH ranges from 7.0 to 8.7 and specific conductance ranges from 13 to 92 µS/cm.


Lake McDonald, Glacier National Park, Montana: type locality of Encyonopsis montana.

Credit/Source: Glacier National Park webcam.


- Correction of taxon name

The specimens illustrated here were originally posted (11.28.2012) on the Diatoms of the US site as Encyonopsis cesati var. geitleri. Further investigation showed that the specimens were not of the type, but of a new species. That species was described as E. montana Bahls 2013. The correction to the taxon name was made. - L. Bahls

- Split of taxon to narrow concept

The specimens illustrated here were earlier posted (09.01.2013) on the Diatoms of the US site as Encyonopsis montana together with two smaller specimens that were subsequently determined to belong to E. cesatiformis. The two smaller specimens have been moved to a new page for E. cesatiformis. - L. Bahls