• Category
  • Length Range
    7-21 µm
  • Width Range
    4-6 µm
  • Striae in 10 µm
  • Synonyms
    Fragilaria binodis Ehrenb.
    Staurosira construens var. binodis (Ehrenb.) Hamilton



Valves are biundulate in larger specimens and lanceolate to cruciform in smaller ones, 4-6 µm wide and 7-21 µm long. Valves with rostrate to subcapitate ends. The central margin is constricted in larger specimens or inflated in smaller specimens. The valve face is flat, or slightly undulate due to raised costae. The valve face/mantle junction forms a sharp angle. The abvalvar edge of mantle is parallel to the valve face/mantle junction. In girdle view, frustules are rectangular. Cells form ribbon-like colonies joined by linking spines. One frustule within a colony is attached to the substratum by a mucilage pad. Cells may also be planktonic. The axial area is broad and linear or slightly lanceolate. The striae are distinct, alternate, and composed of lineolae which decrease in size from the valve face/mantle edge to both the central sternum and the valve mantle; 13-16 in 10 µm. Lineolae bear finely branched volae. The striae are parallel to radiate in the central area. Near the valve ends, the striae are slightly radiate to parallel. Striae extend deep onto the valve mantle. Costae are broad. Spines are spatulate, hollow and some possess terminal digitations that attach to neighboring valve lineolae. Spines are present along the valve face edge, except at the apices, and always located on the costae between striae. Well-developed, ocellulimbus type, apical pore fields with round poroids are present. Apical pore fields are located on the valve mantle. Rimoportula are absent. Scab-like structures, or blisters, are present along the abvalvar side of valve mantle. Copulae lack perforations. Valvocopulae wider than copulae.


Cells form ribbon-like colonies.

Original Description

Sr. construens, testula minima laevis, angulis productis subaequalibus.

  • Basionym
    Fragilaria binodis
  • Author

Original Images

S Construens Binodis  Iconotype


Aug 19, 2021 - Update of nomenclature

From October 24, 2010 to August 18, 2021, this taxon appeared as Staurosira construens var. binodis (Ehrenb.) Hamilton 1992. The name was updated to Staurosira binodis (Ehrenb.) Lange-Bert. in Hofmann et al. based on the transfer by Hofmann, Werum and Lange-Bertalot 2011 (pg 260). - S. Spaulding

Cite This Page

Morales, E. (2010). Staurosira binodis. In Diatoms of North America. Retrieved April 21, 2024, from https://diatoms.org/species/staurosira_binodis


The 15 response plots show an environmental variable (x axis) against the relative abundance (y axis) of Staurosira binodis 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.