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Aulacoseira granulata

(Ehrenb.) Simonsen 1979      Category: Centric
BASIONYM: Gaillonella granulata Ehrenb. 1843
SYNONYM(S): Melosira granulata (Ehrenb.) Ralfs in A.Pritch. 

Aulacoseira crassipunctata


Aulacoseira granulata var. angustissima

LM scalebar = 10 µm = 40 pixels.


Contributor: Marina Potapova | Jonathan English - December 2010
Diameter: 4-17 µm
Mantle Height: 4-20 µm
Rows of areolae in 10 µm: 8-18


Frustules are cylindrical, join face-to-face and form filamentous colonies. Valves are 4-17 µm in diameter, with a mantle height of 4-20 µm. The ratio of the mantle height to valve diameter is usually greater than 0.8 but less than 5. The mantle has straight sides and the valve face is flat. The mantle areolae are square. The rows of areolae on the mantle are curved to the right (dextrorse), but often are almost straight and parallel to pervalvar axis in separation valves and number 8-18 in 10 µm. The valve face has small scattered areolae more densely distributed around the valve face margin. Linking spines are located at the end of each pervalvar costa. Linking spines are short, triangular or bifurcated. Separation spines originate from two pervalvar costae. Most separation spines are 2-6 µm long, but a few, usually 1-2 spines per valve, are very long, almost equal in length to the valve mantle. The ringleiste is solid and moderately shallow. Coiled rimoportulae are usually positioned along a stria on the mantle at the distance of 1-3 areolae from the collum and and similarly along a stria, but much closer to the valve face.

Density and arrangement of the mantle areolae varies considerably among populations and even among cells within a single colony depending on environmental conditions (Stoermer et al. 1981). For the populations found in the Great Lakes the following informal classification of morphotypes was proposed by Stoermer et al. (1981): status α specimens have coarse areolae (8-12 rows in 10 µm, 8-12 areolae in 10 µm in a row) and usually straight rows in separation valves, but spiral in linking valves; status γ specimens have fine areolae (13-18 rows in 10 µm, 13-18 areolae in 10 µm in a row) have only spiral rows of areolae; status β specimens have both types of valves within a colony.

Populations with long thin cells approximately 3-4 µm in diameter have been described as A. granulata var. angustissima (Otto Müller) Simonsen, but Kilham & Kilham (1975) showed that this, as well as another variety A. granulata var. ionensis (Grunow) Simonsen represent morphological variations within the life cycle of A. granulata. We observed a break in the distribution of valve diameters and mantle height/valve diameter ratios in natural populations of A. granulata sensu lato from the US, and for that reason recommend separating the variety angustata from the nominate variety until additional studies clarify the taxonomy of this species complex. No break is observed, however, in the distribution of valve diameters and mantle height/valve diameter ratios between A. granulata and A. muzzanensis, and all other characters appear to overlap between two species. Until further studies clarify the taxonomy of this species complex, we recommend differentiating these two species using this decision rule: if the ratio of the mantle height to valve diameter in at least some cells in a colony is less than 0.8, or if it is between 0.8 and 1.2 and areolae are coarse and disorganized, a specimen is identified as A. muzzanensis. If this ratio in all cells is greater than 0.8, or it is between 0.8 and 1.2, but areolae are organized in regular rows, it is identified as A. granulata.

Colonies are usually straight, but sometimes spiral, with curved cells. Such populations have been described as separate forms of A. granulata (A. granulata f. curvata (Hustedt) Simonsen) and A. granulata f. spiralis (Hustedt) Czarnecki & Reinke, but there is no evidence that this trait has taxonomic significance.

Original Description

Basionym: Gaillonella granulata
Author: Ehrenb. 1843
Diameter: µm
Rows of areolae in 10 µm:

Original Description

G. granulata, articulis coarctatis, tota superficie lineis punctatis transversis (catenarum longitudinalibus) varia, habitu G. aurichalceae.

Original Images

Cite This Page:
Potapova, M., and English, J. (2010). Aulacoseira granulata. In Diatoms of the United States. Retrieved May 24, 2018, from

Species: Aulacoseira granulata

Contributor: Marina Potapova | Jonathan English

Reviewer: Mark Edlund


Davey, M.C. and Crawford, R.M. (1986). Filament formation in the diatom Melosira granulata. Journal of Phycology 22: 144-150.

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.

Gómez, N., Riera, J.L., Sabater, S. (1995). Ecology and morphological variability of Aulacoseira granulata (Bacillariophyceae) in Spanish reservoirs . Journal of Plankton Research 17: 1-16. 10.1093/plankt/17.1.1

Kilham, S.S. and Kilham, P. (1975). Melosira granulata (Ehr.) Ralfs: morphology and ecology of a cosmopolitan freshwater diatom. Verh. Internat. Verein. Limnol. 19: 2716-2721.

Müller, O. (1903). Sprungweise Mutation bei Melosireen. Ber. Dtsch. Bot. Ges. 21, 326-333.

O'Farrell, I., Tell, G., Podlejski, A. (2001). Morphological variability of Aulacoseira granulata (Ehr.) Simonsen (Bacillariophyceae) in the Lower Paraná River (Argentina). Limnology 2: 65-71. 10.1007/s102010170001

Simonsen, R. (1979). The diatom system: ideas on phylogeny. Bacillaria 2: 9-71.

Stoermer, E.F., Kreis Jr., R.G. and Sicko-Goad, L. (1981). A systematic, quantitative, and ecological comparison of Melosira islandica O. Mull. with M. granulata (Ehrenberg) Ralfs from the Laurentian Great Lakes. J. Great Lakes Res. 7: 345-356.

Links & ID's

Index Nominum Algarum (INA)

Transfer INA

California Academy of Sciences (CAS)

Aulacoseira granulata CAS

NCBI Genbank Taxonomy

Aulacoseira granulata NCBI

North American Diatom Ecological Database (NADED)

NADED ID: 10018

Autecology Discussion


A filament of Aulacoseira granulata from Lake Okoboji, Iowa


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

Aulacoseira granulata

EMAP Response Plots

Aulacoseira granulata

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.