• Category
  • Length Range
    60-72 µm
  • Width Range
    2-3 µm
  • Striae in 10 µm



Valves are lanceolate with capitate ends. The central area is wider than rest of the valve. The valve margins may be undulate, with a central swollen middle of the valve. The valve face is undulate due to raised virgae. The valve face/mantle junction forms a sharp angle. The abvalvar edge of the mantle is shallower toward the valve apices, producing detachment of contiguous cells in girdle view. In girdle view, frustules are lanceolate, wider near the center of the valve. Cells form ribbon-like colonies joined by linking spines. The axial area is lanceolate, with clear fascia at the central area. Striae are distinct, composed of apically elongated areolae (lineolae). Striae are interrupted by spines. Striae are parallel throughout the valve and extend midway onto the valve mantle. Costae are wider than the striae. Spines are dimorphic; spatulate near the valve center and conical near the valve ends. Spines are present along the valve face margin, positioned in line with the striae. Well-developed apical pore fields with round poroids are present on the mantle at both valve ends. One rimoportulae is present on each valve. The rimoportula is located along a stria, close to the axial area. Copulae, or girdle bands, were not observed.


Fragilaria crotonensis is a common species in temperate, mesotrophic lakes of North America. Cells can be joined in large ribbon-like colonies. These colonies are resistant to sinking in the water column and help F. crotonensis maintain position in the phytoplankton.

Fragilaria crotonensis, along with Asterionella formosa, is considered a marker that the levels of reactive nitrogen (Nr) have increased above the threshold in oliogotropic lakes of the western United States where diatom assemblages become more like assemblages in mesotrophic and eutrophic lakes (Saros et al. 2005, Wolfe et al. 2006, Spaulding et al. 2015). See the autecology of A. formosa for further discussion.

Fragilaria Crotonensis
Credit: S. Spaulding
Living colony of F. crotonensis.

Original Description

Fragillaria crotonensis, n.s., F. Kitton.-Frustules linear, inflated at the central part, where they cohere and form ribbon-like filament; valve narrow, acicular; striae faint, moniliform (fig.81).-Croton water, New York, Dr. Edwards.

  • Author
    Kitton 1869

Original Images

Fragilaria cotonensis orig illus
F Crotonensis Orig Des

Cite This Page

Morales, E., Rosen, B., Spaulding, S. (2013). Fragilaria crotonensis. In Diatoms of North America. Retrieved May 30, 2024, from https://diatoms.org/species/fragilaria_crotonensis


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