Fragilariforma virescens

(Ralfs) D.M.Williams and Round 1988      Category: Araphid
BASIONYM: Fragilaria virescens Ralfs 1843
SYNONYM(S): Neofragilaria virescens (Ralfs) D.M.Williams and Round 1987 

Fragilariforma polygonata


Frickea lewisiana

LM scalebar = 10 µm = 80 pixels.


Contributor: Eduardo A. Morales | Sarah Spaulding - October 2011
Length Range: 15-60 µm
Width Range: 6.5-7.0 µm
Striae in 10 µm: 20-22


Valves linear to lanceolate with parallel or convex sides. Valves with rostrate, broadly rounded ends. The central area is narrow and linear. The valve face is flat. The valve face/mantle junction forms a sharp angle. The abvalvar edge of the mantle is parallel to the valve face/mantle junction. In girdle view, frustules are rectangular. Cells form short ribbon-like colonies, joined by linking spines. The axial area is linear. Striae are distinct, composed of round areolae. Areolae are uniform in size from axial area to valve mantle. Striae are parallel throughout the valve, and extend continuously onto the valve mantle, stopping shortly before the abvalvar mantle edge. Costae are wider than the striae. Spines are spatulate. Spines are present along the valve face edge, including the apices, and are located on the costae between striae. Well-developed, simple type, apical pore fields with round poroids are present. Pore fields are located on the junction between valve face and mantle. One rimoportula is present on each valve, located along a stria close to the axial area, expressed internally as a small labium. Copulae, or girdle bands, were not observed.

Original Description

Basionym: Fragilaria virescens
Author: Ralfs 1843
Length Range: µm
Striae in 10 µm:

Original Description

F. virescens. Frustules broad, with two evident puncta at each end; lateral surfaces turgid-lanceolate, constricted near the ends; striae none, or indistinct. Frag. pectinalis, Ehrenb. Die. Infus. p. 206. t. 6. fig. 1; Ptrich. Infus. p. 222. fig. 176.

Original Images

Cite This Page:
Morales, E., and Spaulding, S. (2011). Fragilariforma virescens. In Diatoms of the United States. Retrieved April 19, 2018, from

Species: Fragilariforma virescens

Contributor: Eduardo A. Morales | Sarah Spaulding

Reviewer: Rex Lowe


Ralfs, J. (1843). On the Diatomaceae. Annals and Magazine of Natural History 12: 104-111, pl. 2.

Van Heurck, H. (1881). Synopsis des Diatomées de Belgique. Atlas. Ducaju & Cie., Anvers. pls 31-77.

Williams, D.M. (2001). Comments on the structure of “post-auxospore” valves of Fragilariforma virescens. In: Jahn, R., Kociolek, J.P., Witkowski, A and Compère, P. (eds), Lange-Bertalot-Festschrift: Studies on Diatoms. Dedicated to Prof. Dr. Dr. h.c. Horst Lange-Bertalot on the occassion of his 65th Birthday. A.R.G. Gantner Verlag. K.G. pp. 103-117.

Williams, D.M. and Round, F.E. (1988). Fragilariforma, nom. nov., a new generic name for Neofragilaria Williams & Round. Diatom Research 3: 265-267.

Links & ID's

Index Nominum Algarum (INA)

Original INA
Transfer INA

California Academy of Sciences (CAS)

Fragilariforma virescens CAS
Fragilariforma virescens CAS

NCBI Genbank Taxonomy

Fragilariforma virescens NCBI

North American Diatom Ecological Database (NADED)

NADED ID: 192008

Autecology Discussion

Frustules are linked by marginal spines to form colonies.

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

Fragilariforma virescens

EMAP Response Plots

Fragilariforma virescens

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.