Chamaepinnularia mediocris

(Krasske) Lange-Bert. in Lange-Bert. and Metzeltin 1996      Category: Symmetrical biraphid
BASIONYM: Navicula mediocris Krasske 1932
SYNONYM(S): Pinnularia mediocris (Krasske) Mills 1935 

Chaetoceros muelleri


Chamaepinnularia soehrensis

LM scalebar = 10 µm = 80 pixels.


Contributor: Megan Otu | Sarah Spaulding - March 2011
Length Range: 9-16 µm
Width Range: 2.7-3.0 µm
Striae in 10 µm: 20-24


Valves are linear to broadly oval, with rounded apices and a gibbous middle. The axial area is narrow near the apices, becoming wider near the central area. The central area is a transverse fascia: in some specimens it extends to the valve margins, in other specimens short irregular striae are present at the margins. The raphe is filiform and slightly arched. Terminal nodules are distinct. The striae are parallel and composed of a single, elongate areola on the valve face. A smaller areola is positioned on the valve mantle. Externally, the proximal raphe ends are straight. Internally, the proximal raphe ends are slightly deflected unilaterally.

Original Description

Basionym: Navicula mediocris
Author: Krasske 1932
Length Range: 9-12 µm
Width Range: 2,5-3 µm
Striae in 10 µm: 22-24

Original Description

Schalen linear mit bauchiger Mitte und gerundeten Enden. Streifen krätfig, die beiden mittleren schwächer, parallel, 22-24 in 10 µ. Area schmal, in der Mitte rundlich erweitert. Raphe sehr zart. Lang 9-12 µ, breit 2,5-3 µ.

Original Images

Cite This Page:
Otu, M., and Spaulding, S. (2011). Chamaepinnularia mediocris. In Diatoms of the United States. Retrieved April 23, 2018, from

Species: Chamaepinnularia mediocris

Contributor: Megan Otu | Sarah Spaulding

Reviewer: Loren Bahls


Krasske, G. (1932). Beiträge zur Kenntnis der Diatomeenflora der Alpen. Nova Hedwigia 72(3): 92-135.

Lange-Bertalot, H. and Metzeltin, D. (1996). Indicators of oligotrophy - 800 taxa representative of three ecologically distinct lake types, Carbonate buffered - Oligodystrophic - Weakly buffered soft water. Lange-Bertalot, H. (ed.), Iconographia Diatomologica. Annotated Diatom Micrographs. Vol. 2. Ecology, Diversity, Taxonomy. Koeltz Scientific Books. Königstein, Germany, 2:390 pp.

Lange-Bertalot, H., Kulbs, K., Lauser, T., Norpel-Schempp, M. and Willmann, M. (1996). Diatom taxa introduced by Georg Krasske: Documentation and revision. Iconographia Diatomologica (H. Lange-Bertalot, ed.), Vol. 3, Koeltz Scientific Books, Konigstein, 358 pp.

Links & ID's

Index Nominum Algarum (INA)

Original INA

California Academy of Sciences (CAS)

Chamaepinnularia mediocris CAS

North American Diatom Ecological Database (NADED)

NADED ID: 212005

Autecology Discussion

Chamaepinnularia mediocris is found in oligotrophic waters of the US. On the main identification page we document images of specimens from Maine, Pennsylvania and Wyoming. This species was relatively uncommon in the western EMAP survey of US streams and rivers, and never occurred in high relative abundance.The cells from high elevation lakes of Grand Teton National Park are at the small end of the size spectrum, while cells from the eastern US are larger. In the western EMAP survey, C. mediocris was found at pH between 7 and 8.


Holly Lake, in Grand Teton National Park, Wyoming, is one of the high elevation lakes where Chamaepinnularia mediocris is found.

Credit/Source: Sarah Spaulding

EMAP Assessment

The Environmental Protection Agency (EPA) western Environmental Monitoring and Assessment Program (EMAP) study was completed during the years 2000-2004 (see citations at bottom of this page). Over 1200 streams and rivers in 12 western states (Arizona, California, Colorado, Idaho, Montana, Nevada, North Dakota, Oregon, South Dakota, Utah, Washington and Wyoming) were selected for sampling based on a stratified randomized design. This type of design insures that ecological resources are sampled in proportion to their actual geographical presence. Stratified randomized design also allows for estimates of stream length with a known confidence in several “condition classes” (good or least-disturbed, intermediately-disturbed, and poor or most-disturbed) for biotic condition, chemistry and habitat.

EMAP Distribution

Chamaepinnularia mediocris

EMAP Response Plots

Chamaepinnularia mediocris

EMAP citations

Results are published in:

Johnson, T., Hermann, K., Spaulding, S., Beyea, B., Theel, C., Sada, R., Bollman, W., Bowman, J., Larsen, A., Vining, K., Ostermiller, J., Petersen, D. Hargett, E. and Zumberge, J. (2009). An ecological assessment of USEPA Region 8 streams and rivers. U.S. Environmental Protection Agency Region 8 Report, 178 p.

Stoddard, J. L., Peck, D. V., Olsen, A. R., Larsen, D. P., Van Sickle, J., Hawkins, C. P., Hughes, R. M., Whittier, T. R., Lomnicky, G. A., Herlihy, A. T., Kaufman, P. R., Peterson, S. A., Ringold, P. L., Paulsen, S. G., and Blair, R. (2005). Environmental Monitoring and Assessment Program (EMAP) western streams and rivers statistical summary. U.S. Environmental Protection Agency Report 620/R-05/006, 1,762 p.

Stoddard, J. L., Peck, D. V., Paulsen, S. G., Van Sickle, J., Hawkins, C. P., Herlihy, A. T., Hughes, R. M., Kaufman, P. R., Larsen, D. P., Lomnicky, G. A., Olsen, A. R., Peterson, S. A., Ringold, P. L., and Whittier, T. R. (2005). An ecological assessment of western streams and rivers. U.S. Environmental Protection Agency Report 620/R-05/005, 49 p.