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Diatoms of the United States is now known as Diatoms of North America.
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Eunotia serra

Ehrenb. 1837      Category: Eunotioid

Eunotia sarraceniae


Eunotia spatulata

LM scalebar = 10 µm = 20 pixels.


Contributor: Loren Bahls - July 2012
Length Range: 60-134 µm
Width Range: 18-24 µm
Striae in 10 µm: 9-13 in the valve center, 14-19 near the apices


Valves are very large and highly arched. The dorsal margin has 9 to 16 bluntly pointed and evenly spaced undulations. The ventral margin is concave and follows the same curvature as the dorsal margin. Valve apices are about the same size and shape as the undulations (images 1 and 3). Occasionally a terminal undulation will coalesce with the apex, which then becomes much wider and obtusely rounded (images 2 and 7). Distal raphe ends terminate about two thirds of the way from the ventral to the dorsal margin and at some distance from the apex. Striae are radiate throughout and of two types: complete striae that extend the full width of the valve and short striae that occur only along the dorsal margin. Short dorsal striae are more frequent within the undulations, especially in smaller specimens. A fine transparent line runs along the ventral margin and ascends the valve face near the apices, where it angles towards the terminal nodules. Striae on either side of this line may be continuous or displaced. Areolae in the striae are 26-29 in 10 µm.

The number of dorsal undulations in other U.S. populations ranges from 6 to 22, valve length ranges from 40 to 165 µm, and valve width ranges from 13 to 18 µm (Brant & Furey 2011, P. C. Furey, pers. comm.). Montana specimens (18-24 µm wide) are wider than these and also wider than specimens reported from Europe (12-16 µm wide; Lange-Bertalot et al. 2011).

Original Description

Author: Ehrenb. 1837
Length Range: µm
Striae in 10 µm:

Original Description

Original Images

Cite This Page:
Bahls, L. (2012). Eunotia serra. In Diatoms of the United States. Retrieved May 22, 2018, from

Species: Eunotia serra

Contributor: Loren Bahls

Reviewer: Paula Furey


Brant, L.A. and Furey, P.C. (2011). Morphological variation in Eunotia serra, with a focus on the rimoportula. Diatom Research 26(2): 221-226. 10.1080/0269249X.2011.601326

Ehrenberg, C.G. (1837). Über ein aus fossilen Infusorien bestehendes, 1832 zu Brod verbacknes Bergmehl von der Grenzen Lapplands in Schweden. Bericht über die zur Bekanntmachung geeigneten Verhandlungen der Königlich-Preussischen Akademie der Wissenschaften zu Berlin 1837:43-45.

Krammer, K. and Lange-Bertalot, H. (1991). Bacillariophyceae. 3. Teil: Centrales, Fragilariaceae, Eunotiaceae. In Ettl, H., Gerloff, J., Heynig, H. & Mollenhauer, D. (Eds.). Süsswasserflora von Mitteleuropa. 2(3): 1-576. Gustav Fisher Verlag, Stuttgart, Germany.

Lange-Bertalot, H., Bak, M., Witkowski, A. and Tagliaventi, N. (2011). Eunotia and some related genera. Diatoms of the European Inland Waters and Comparable Habitats. 6: 747 pp.

Patrick, R.M. and Reimer, C.W. (1966). The Diatoms of the United States exclusive of Alaska and Hawaii, V. 1. Monographs of the Academy of Natural Sciences of Philadelphia 13.

Links & ID's

Index Nominum Algarum (INA)

Original INA

California Academy of Sciences (CAS)

Eunotia serra CAS

North American Diatom Ecological Database (NADED)

NADED ID: 33054

Autecology Discussion

Eunotia serra has been reported from a number of lakes and bogs in the central and northeastern United States, as well as Gulf Coast states, Colorado, and California (Brant & Furey 2011, Patrick & Reimer 1966). These sites typically have acidic pH and very low electrical conductivity. Lange-Bertalot et al. (2011) report this species as a component of the Holarctic flora of Eurasia and North America. In the Northern Rockies, E. serra has been recorded from ponds and small lakes in the Bitterroot Range on the Montana/Idaho border. Here pH ranges from 5.5 to 6.5 and EC ranges from 5 to 27.


Blodgett Lake in the Bitterroot Range, Selway-Bitterroot Wilderness, Ravalli County, Montana: home of Eunotia serra.

Credit/Source: R. A. Carlsen

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

Eunotia serra

EMAP Response Plots

Eunotia serra

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.