Pseudostaurosira trainorii

E.Morales 2001      Category: Araphid

REPORTED AS: Staurosira elliptica ((Schumann) Williams and Round 1987) | Fragilaria elliptica (Schumann) 

Pseudostaurosira robusta


Punctastriata mimetica

LM scalebar = 10 µm = 80 pixels.


Contributor: Eduardo A. Morales - April 2013
Length Range: 2-9 µm
Width Range: 1.5-4.5 µm
Striae in 10 µm: 18-25


Cells are rectangular in girdle view and form ribbon-like colonies joined by linking spines. Valves are round to slightly elliptical. The valve face is flat, or slightly undulate due to raised costae. Valve face/mantle junction forms a sharp angle. Abvalvar edge of mantle in middle portion of valve is convex with respect to the valve face/mantle junction. The axial area is narrow to widely lanceolate, or may be linear in some specimens. Striae are distinct, alternate, and composed of round areolae decreasing in size from valve face/mantle edge to both central sternum and valve mantle. Areolae bear finely and profusely branched volae. Flaps partially cover the external opening of the areolae, especially on mantle areolae. Striae vary from parallel to radiate. Striae extend onto the valve mantle, further in smaller specimens. Costae are broad and wider than striae. Spines are spatulate, solid, possess a serrate margin and bear flaps at the base, which cover the openings of the contiguous areolae. Spines are positioned within the striae at the valve face/mantle junction. Apical pore fields absent, or reduced to two to three pores located on valve face/mantle junction. Rimoportula are absent. Scab-like structures, or blisters, are present in some specimens as depositions on the abvalvar edge of mantle. Copulae are open and lack perforations. Valvocopula are wider than other copulae. Plastids were not observed.

This taxon has been commonly reported as Staurosira elliptica (Schumann) Williams and Round. This was due to a misinterpretation of the type of Fragilaria elliptica Schumann. The type of F. elliptica has been evaluated (Edlund et al. 2006) and not only is it better placed in the genus Pseudostaurosira, Staurosira elliptica has not been confirmed in North America. Pseudostaurosira elliptica (Schumann) Edlund et al. has elliptical valves with acute ends, striae restricted to the valve margin, but lacks serrate spines - all features differ from those of P. trainori.

Original Description

Author: E.Morales 2001
Length Range: 2-9 µm
Width Range: 1.5-4.5 µm
Striae in 10 µm: 18-25

Original Description

Original Images

Cite This Page:
Morales, E. (2013). Pseudostaurosira trainorii. In Diatoms of the United States. Retrieved April 21, 2018, from

Species: Pseudostaurosira trainorii

Contributor: Eduardo A. Morales

Reviewer: Marina Potapova


Edlund, M.B., Morales, E.A. and Spaulding, S.A. (2006). The type and taxonomy of Fragilaria elliptica Schumann, a widely misconstrued taxon. In: Witkowski, A. (Ed.). Proceedings of the 18th International Diatom Symposium. Miedzyzdroje, Poland. pp 53-59. Biopress Limited, Bristol, England.

Morales, E.A. (2001). Morphological studies in selected fragilarioid diatoms (Bacillariophyceae) from Connecticut waters (U.S.A.). Proceedings of the Academy of Natural Sciences of Philadelphia 151: 105-120.

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

Links & ID's

Index Nominum Algarum (INA)

California Academy of Sciences (CAS)

Pseudostaurosira trainorii CAS

North American Diatom Ecological Database (NADED)

NADED ID: 73013

Autecology Discussion

Colonies are presumably attached to the substratum at one end by a frustule attached by a mucilage pad, or planktonic.

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 trainorii

EMAP Response Plots

Pseudostaurosira trainorii

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.