Pseudostaurosira robusta

(Fusey) D.M.Williams and Round 1988      Category: Araphid
BASIONYM: Fragilaria construens var. binodis f. robusta Fusey 1953
SYNONYM(S): Fragilaria robusta (Fusey) Manguin | Staurosira robusta (Fusey) Lange-Bert. 

Pseudostaurosira pseudoconstruens


Pseudostaurosira trainorii

LM scalebar = 10 µm = 80 pixels.


Contributor: Ian Bishop - July 2015
Length Range: 13-17 µm
Width Range: 2.6-4.1 µm
Striae in 10 µm: 14-16


Valves are bi-undulate, with rounded sub-capitate to capitate ends. Valves are 13-17 µm in length, 3.6-4.1 µm in width. The axial area is wide and linear to lanceolate. In some specimens, the axial area is nearly as wide as the central constriction. Striae are 14-16 in 10 µm and uniseriate. The striae are composed of round, coarse areolae that number 14-16 in 10 µm. Valves link to form band-like colonies, and these colonies are distinct in girdle view.

This taxon was found in the H.E. Sovereign Collection at the California Academy of Sciences (CAS 184007). In this material, P. robusta co-occurs with the similar, uni-undulate P. pseudoconstruens, along with specimens that are asymmetric in their undulations. That is, the asymmetric specimens have “one hump” on one margin of the valve, and “two humps” on the other margin. I investigated this material to determine if the two taxa could actually be a single taxon, along a size spectrum (see graphics in Autecology Section). From this sample, it appears that the asymmetric specimens are associated with P. robusta. However, these observations are not conclusive and it is possible that there is a positive relationship between size and valve undulation, implying that the two taxa should be combined. Further examination of their systematic relationship is encouraged.

Original Description

Basionym: Fragilaria construens var. binodis f. robusta
Author: Fusey 1953
Length Range: 10-18 µm
Width Range: 2.5-4.5 µm
Striae in 10 µm: 14-16

Original Description

F. construens var. binodis (Ehr.) Grun, f. robusta f. nov. (Pl. 1, fig. 2) 9. Valve nettement étranglée au centre, extrémités étirées, légèrement subcapitées. 10-18μ x 4-6μ, 2,5-4,5μ au centre; area central vaste - stries robustes, fortement ponctuées, 14-16 en 10μ.

Original Images

Cite This Page:
Bishop, I. (2015). Pseudostaurosira robusta. In Diatoms of the United States. Retrieved April 22, 2018, from

Species: Pseudostaurosira robusta

Contributor: Ian Bishop

Reviewer: Eduardo A. Morales


Fusey, P. (1951). Contribution à la flore algologique de Bretagne. Diatomées de la Region de Corlay (Côte-du-Nord). Bulletin de microscopie appliquée 2(1): 31-50.

Williams, D.M. and Round, F.E. (1987). Revision of the genus Synedra Ehrenb. Diatom Research 1(2): 313-339.

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

California Academy of Sciences (CAS)

Pseudostaurosira robusta CAS

North American Diatom Ecological Database (NADED)


Autecology Discussion

To date, P. robusta has been recorded in surveys of rivers (USGS NAWQA program) in the western US, including California, Nevada, Idaho, Washington, Nebraska, Wyoming and Alaska.


Valves of P. pseudoconstruens, an asymmetric hybrid valve, and P. robusta, organized by size, from left to right, top to bottom. Scale bar: 10 µm.

Credit/Source: Specimens photographed by Drew Meyer, composite image by Ian Bishop

Histograms of P. pseudoconstruens (top, in green), an asymmetric morphology (middle, in blue), and P. robusta (bottom, in orange).

Credit/Source: Graphic by Ian Bishop

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

Pseudostaurosira robusta

EMAP Response Plots

Pseudostaurosira robusta

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.