• Category
  • Length Range
    13.3-17.1 µm
  • Width Range
    2.6-4.1 µm
  • Striae in 10 µm
  • Synonyms
    Fragilaria robusta (Fusey) Manguin
    Staurosira robusta (Fusey) Lange-Bert.



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.


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.

Credit: Specimens photographed by Drew Meyer, composite image by Ian Bishop
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: Graphic by Ian Bishop
Histograms of P. pseudoconstruens (top, in green), an asymmetric morphology (middle, in blue), and P. robusta (bottom, in orange).

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.

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

Original Images

Pseudostaurosira Robusta  Fusey  Image 1951
Pseudostaurosira Robusta  Fusey  Text 1951

Cite This Page

Bishop, I. (2015). Pseudostaurosira robusta. In Diatoms of North America. Retrieved May 29, 2024, from https://diatoms.org/species/pseudostaurosira_robusta


The 15 response plots show an environmental variable (x axis) against the relative abundance (y axis) of Pseudostaurosira robusta from all the stream reaches where it was present. Note that the relative abundance scale is the same on each plot. Explanation of each environmental variable and units are as follows:

ELEVATION = stream reach elevation (meters)
STRAHLER = distribution plot of the Strahler Stream Order
SLOPE = stream reach gradient (degrees)
W1_HALL = an index that is a measure of streamside (riparian) human activity that ranges from 0 - 10, with a value of 0 indicating of minimal disturbance to a value of 10 indicating severe disturbance.
PHSTVL = pH measured in a sealed syringe sample (pH units)
log_COND = log concentration of specific conductivity (µS/cm)
log_PTL = log concentration of total phosphorus (µg/L)
log_NO3 = log concentration of nitrate (µeq/L)
log_DOC = log concentration of dissolved organic carbon (mg/L)
log_SIO2 = log concentration of silicon (mg/L)
log_NA = log concentration of sodium (µeq/L)
log_HCO3 = log concentration of the bicarbonate ion (µeq/L)
EMBED = percent of the stream substrate that is embedded by sand and fine sediment
log_TURBIDITY = log of turbidity, a measure of cloudiness of water, in nephelometric turbidity units (NTU).
DISTOT = an index of total human disturbance in the watershed that ranges from 1 - 100, with a value of 0 indicating of minimal disturbance to a value of 100 indicating severe disturbance.