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

W.Sm. ex W.Greg. 1854      Category: Eunotioid

Eunotia horstii


Eunotia kociolekii

LM scalebar = 10 µm = 80 pixels.


Contributor: Paula Furey - December 2011
Length Range: 12-50 µm
Width Range: 2.8-5.0 µm
Striae in 10 µm: 16-21 in the center valve


The ventral margin is straight in smaller specimens and weakly concave in larger specimens. The dorsal margin is convex. The apices are acutely rounded, appearing ‘nose-like’ due to the inset position of the helictoglossae. The helictoglossae are set in equidistant from the apices (symmetric to the transapical axis), giving the appearance of an indentation in the LM. One apical rimoportula is present, just dorsal to the center of the apex, and is expressed externally as a round pore. The distal ends of the raphe lie on the valve mantle and the terminal raphe nodules are well set in from the apices. In girdle view the frustules are rectangular to quadratic and the inset helictoglossae are observable.

Several forms and variations in length (L), width (W) and stria density are currently included in the broad concept of E. incisa as presented by Patrick and Reimer (1966; L 15-50 µm, W 4-7 µm, 13-17 stria/10 µm), Krammer and Lange-Bertalot (1991, 13-50 µm, W 4-6 µm, 12-17 stria/10 µm), Siver et al. (2005, L 12-28 µm, W 3-4 µm, 16-17 stria/10 µm; also narrow specimens W 2-2.5 µm), and Furey et al. (2011, 13-50 µm, W 2.8-5.0 µm, 12-17 stria/10 µm). Some of the narrow specimens have been described as new species, such as E. canicula. Specimens that have broader, more rounded apices, such as valves similar in form to Taf. 161, Figs 13-15 in Krammer and Lange-Bertalot (1991) may later be described as new species, but for now should be tracked as a variation in valve form. Lange-Bertalot et al. (2011) have further described new species from Europe, such as E. incisadistans, that share similarities in form (including the inset helictoglossae) that should be compared with the North American flora as taxonomic work on this species continues. Eunotia incisadistans has broader valves with lower stria density.

Original Description

Author: W.Sm. ex W.Greg. 1854
Length Range: µm
Striae in 10 µm:

Original Description

Original Images

Cite This Page:
Furey, P. (2011). Eunotia incisa. In Diatoms of the United States. Retrieved May 22, 2018, from

Species: Eunotia incisa

Contributor: Paula Furey

Reviewer: Marina Potapova


Furey, P.C., Lowe, R.L. and Johansen, J.R. (2011). Eunotia Ehrenberg (Bacillariophyta) of the Great Smoky Mountains National Park, USA. Bibliotheca Diatomologica 56: 1-134.

Gregory, W. (1854). Notice of the new forms and varieties of known forms occurring in the diatomaceous earth of Mull; with remarks on the classification of the Diatomaceae. Quarterly Journal of Microscopical Science, London 2: 90-100.

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.

Metzeltin, D. and Lange-Bertalot, H. (1998). Tropical diatoms of South America I: About 700 predominantly rarely known or new taxa representative of the neotropical flora. In: Lange-Bertalot, H. (ed.), Iconographia Diatomologica. Annotated Diatom Micrographs. Vol. 5. Diversity-Taxonomy-Geobotany. Koeltz Scientific Books. Königstein, Germany, 5:695 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.

Siver, P.A. and Hamilton, P.B. (2011). Diatoms of North America: The Freshwater Flora of Waterbodies on the Atlantic Coastal Plain. Iconographia Diatomologica 22.

Siver, P.A., Hamilton, P.B., Stachura-Suchoples, K. and Kociolek, J.P. (2005). Diatoms of North America. The Freshwater Flora of Cape Cod. Iconographia Diatomologica 14: 1-463.

Links & ID's

Index Nominum Algarum (INA)

Original INA

California Academy of Sciences (CAS)

Eunotia incisa CAS

North American Diatom Ecological Database (NADED)

NADED ID: 33026

Autecology Discussion

Eunotia incisa is common in acidic, freshwater environments, and can occasionally occur in high abundances.

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 incisa

EMAP Response Plots

Eunotia incisa

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.