Eunotia exigua

(Bréb. in Kütz.) Rabenh. 1864      Category: Eunotioid
BASIONYM: Himantidium exiguum Bréb. in Kütz. 1864

Eunotia eruca


Eunotia faba

LM scalebar = 10 µm = 80 pixels.


Contributor: Paula Furey - March 2012
Length Range: 8-22 µm
Width Range: 1.8-3.2 µm
Striae in 10 µm: 16-24 in the center, 20-24 at the ends


Frustules are narrow rectangles in girdle view. Ventral margin is concave. In smaller specimens the ventral margin is slightly concave or straight. Dorsal margin is convex. Apices are protracted, and frequently strongly dorsally reflexed. Apices of shorter specimens are more obtusely rounded. Helictoglossae are positioned close to the apices. Distal raphe end curves a short distance on to the valve face.

There is some variability in valve morphology of E. exigua between populations. For example, some populations are less silicified than others or the ventral margin is less convex. (compare first two specimens with last four specimens). Lange-Bertalot et al (2011) report broader specimens from Europe (3 to 4 µm) though earlier Krammer and Lange-Bertalot (1991) include narrower specimens (2 ?) 2.5 to 4 (5) µm. Patrick and Reimer (1966) report a range in valve width of 2 to 4 µm.

See further discussion around E. exigua taxonomy in Lange-Bertalot et al. (2011). Eunotia exigua sensu lato, a complex of closely related taxa, has recently had several taxa removed, such as E. cataractarum, E. orthohedra, E. exigua var. tridentula, E. exigua var. undulata, E. kruegeri, and others. Both habitat and a careful examination of valve outline and morphological characteristics will help distinguish taxa. More taxonomic work is needed.

Original Description

Basionym: Himantidium exiguum
Author: Bréb. in Kütz. 1864
Length Range: µm
Striae in 10 µm:

Original Description

H. exiguum. Brébisson in litt. — H. minutum, laevissimum, fascias brevissimas formans, articulis a latere secundario arcuatis, apicibus productis, obtusissimis. — Long. 1/250—1/150´´´. — In Gallia. Specimina comm. amic. De Brébisson (v. s.)

Original Images

Cite This Page:
Furey, P. (2012). Eunotia exigua. In Diatoms of the United States. Retrieved April 24, 2018, from

Species: Eunotia exigua

Contributor: Paula Furey

Reviewer: Marina Potapova


Alles, E., Nörpel-Schempp, M. and Lange-Bertalot, H. (1991). Taxonomy and ecology of characteristic Eunotia species in headwaters with low electric conductivity. Nova Hedwigia 53: 171-213.

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.

Grunow, A. (1862). Die österreichischen Diatomaceen nebst Anschluss einiger neuen Arten von andern Lokalitäten und einer kritischen Uebersicht der bisher bekannten Gattungen und Arten. Erste Folge. Epithemieae, Meridioneae, Diatomeae, Entopyleae, Surirelleae, Amphipleureae. Zweite Folge. Familie Nitzschieae. Verhandlungen der Kaiserlich-Königlichen Zoologisch-Botanischen Gesellschaft in Wien 12: 368, Pl. 7, fig. 8.

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.

Rabenhorst, L.G. (1864). Flora Europaea Algarum aquae dulcis et submarinae. Sectio I. Algas diatomaceas complectens, cum figuris generum omnium xylographice impressis. Eduardum Kummerum, Lipsiae 359 pp.

Links & ID's

Index Nominum Algarum (INA)

Transfer INA

California Academy of Sciences (CAS)

Eunotia exigua CAS

North American Diatom Ecological Database (NADED)

NADED ID: 33015

Autecology Discussion

Eunotia exigua is an indicator of acidic conditions in the Great Smoky Mountains where it is common in streams, waterfalls and wetwalls.

In Europe, taxa included within the E. exigua species complex are considered to occur in sites with anthropogenic acidification (Alles et al. 1991) and found in waters with increased aluminum and sulfate concentrations.

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 exigua

EMAP Response Plots

Eunotia exigua

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.