Aulacoseira granulata var. angustissima

(O.Müll.) Simonsen 1979      Category: Centric
SYNONYM(S): Melosira granulata subsp. angustissima (O.Müll.) A.Cleve 

Aulacoseira granulata


Aulacoseira herzogii

LM scalebar = 10 µm = 40 pixels.


Contributor: Jonathan English | Marina Potapova - December 2010
Diameter: 2.5-4 µm
Mantle Height: 8-20 µm
Rows of areolae in 10 µm: 10-20


Frustules are cylindrical and form colonies. Valves are 2.5-4 µm in diameter, with a mantle height of 8-20 µm. The ratio of the mantle height to valve diameter is greater than 3.2. 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. There are 10-20 rows in 10 µm. The valve faces of most valves do not have areolae, but a single ring of areolae might be found on the valve face of separation valves. Linking spines are located at the end of each pervalvar costa. They are short, bifurcated. Separation spines originate from two pervalvar costae. Most separation spines are 2-6 µm long and broadly triangular, but 1 or 2 spines per valve are very long, almost equal in length to the valve mantle. The ringleiste is solid and moderately shallow.

Kilham & Kilham (1975) showed that A. granulata var. angustissima is a morphological variation within the life cycle of A. granulata, but 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. Specimens with valve diameter 4 µm or less and mantle height/valve diameter ratio greater than 3.2 should be identified as A. granulata var. angustissima, while specimens with either valve diameter greater than 4 µm, or mantle height/valve diameter ratio lower than 3.2, or both, should be placed in the nominate variety.

Note that it is not clear at present whether A. granulata var. angustissima from North America represents the same biological species as the type of this taxon from Africa, but the name has been used by North American workers in the past and is here recommended to be used to maintain consistency.

Original Description

Author: O.Müll. 1900
Diameter: 3 µm
Mantle Height: 30 µm
Rows of areolae in 10 µm: 8-9

Original Description

Discus kreisrund, ohne Dornen, mantel cylindrisch; Sulcus schmal und wenig tief, Ansatzring schwach trichterförmig. Porenreihen in steilen Sprialen angordnet, Poren grob. Membran mittelstark. Porenreihen 8-9 auf 10 μ, Poren in pervalvarer Richtung 10-12 auf 10 μ. Lg. 60 μ, lat. 3 μ.

Original Images

Cite This Page:
English, J., and Potapova, M. (2010). Aulacoseira granulata. In Diatoms of the United States. Retrieved April 22, 2018, from

Species: Aulacoseira granulata

Contributor: Jonathan English | Marina Potapova

Reviewer: Mark Edlund


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. (1900). Bacillariaceen aus den Natronthälern von El Kab (Ober-Aegypten). Hedwigia 38(5-6):274-288, 289-321. .

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

Links & ID's

Index Nominum Algarum (INA)

Original INA

California Academy of Sciences (CAS)

Aulacoseira granulata var. angustissima CAS

NCBI Genbank Taxonomy

Aulacoseira granulata var. angustissima NCBI

North American Diatom Ecological Database (NADED)

NADED ID: 10017

Autecology Discussion

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 var. angustissima

EMAP Response Plots

Aulacoseira granulata var. angustissima

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.