Eunotia formica

Ehrenberg 1843      Category: Eunotioid
BASIONYM: Eunotia formica Ehrenberg 1843

Eunotia faba


Eunotia gibbosa

LM scalebar = 10 µm = 40 pixels.


Contributor: David R.L. Burge | Mark Edlund - August 2015
Length Range: 52-142 µm
Width Range: 6.4–9.9, at the central swelling: 7.8–15.8 µm
Striae in 10 µm: 6–10 in the center, 10–16 near the apices


Valves are weakly arcuate. The dorsal margins are convex and the ventral margins are concave. Most specimens have gibbous swellings observed in the valve center. Apices are weakly capitate, with acutely rounded to cuneate ends. Helictoglossae are present near the apices. Terminal raphe fissures are visible on the valve face, around the apices to the dorsal margin. Striae are perpendicular to the valve margins. Striae are typically regularly spaced, although irregular spacing is common. A sternum is visible near the ventral margin. Areolae are distinct and number 23–28 in 10 µm.

The concept of E. formica presented conforms to the taxon in a broad sense (sensu lato). Lange-Bertalot et al. (2011) draw distinction within European specimens of E. formica, and recognize the species E. formicina and E. myrmica. These species were distinguished based on differences in apicies; rounded in E. formicina and acuminate in E. myrmica. Our specimens overlap in areola density described for E. formica sensu stricto, E. formica sensu lato, E. formicina, and E. myrmica, and show a range of apices from rounded to acuminate. Because we see such notable variation in a single population, we consider the variation to be attributable to phenotypic plasticity within E. formica.

Original Description

Basionym: Eunotia formica
Author: Ehrenberg 1843
Length Range: µm
Striae in 10 µm:

Original Description

E. formica, striata linearis, media parte utrinque et utroque apice turgidis. E. nodosa apicibus non reflexis, sed inflatis rectis.

Original Images

Cite This Page:
Burge, D., and Edlund, M. (2015). Eunotia formica. In Diatoms of the United States. Retrieved October 20, 2017, from

Species: Eunotia formica

Contributor: David R.L. Burge | Mark Edlund

Reviewer: Rex Lowe


Burge, D.R.L. (2014). Relations of water quality, land use buffers, and diatom communities of connected depressions within the Cache River Watershed, Arkansas, USA. M.S. Thesis. Arkansas State University, Jonesboro, Arkansas. 141 pp.

Ehrenberg, C.G. (1843). Verbreitung und Einfluß des mikroskopischen Lebens in Süd- und Nord-Amerika. Abhandlungen der Königlichen Akademie der Wissenschaften zu Berlin, 1841: 291-445, 4 Tafel.

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.

Links & ID's

Index Nominum Algarum (INA)

Original INA

California Academy of Sciences (CAS)

Eunotia formica CAS

NCBI Genbank Taxonomy

Eunotia formica NCBI

North American Diatom Ecological Database (NADED)

NADED ID: 33021

Autecology Discussion

Burge (2014) found E. formica occurring among the epiphyton and benthos of cypress-tupelo wetlands with: 22.2–27.4 C, 5.6–7.4 pH, specific conductivity 71.2–834.0 µS/cm, 8.1–321.0 NTU, DO 0.1–7.7 mg/L, NO3-N 0.01–0.3 mg/L, NO2-N <0.01– 0.05 mg/L, orthophosphate 0.02–2.08 mg/L, and TP 0.11–3.93 mg/L. Other common species were Eunotia bidens, E. bilunaris, E. metamonodon, E. pectinalis, and E. superbidens as well as species of Gomphonema, Navicula, Nitzschia, and Pinnularia.


Distribution of Eunotia formica in the continental U.S. Retrieved 08 May 2015.

Credit/Source: Credit/Source: USGS BioData

Distribution of Eunotia formica in the continental U.S. Retrieved 08 May 2015.

Credit/Source: Credit/Source: USGS BioData

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 formica

EMAP Response Plots

Eunotia formica

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.