• Category
  • Length Range
    15-60 µm
  • Width Range
    6.5-7.0 µm
  • Striae in 10 µm
  • Synonyms
    Neofragilaria virescens (Ralfs) D.M.Williams and Round 1987



Valves linear to lanceolate with parallel or convex sides. Valves with rostrate, broadly rounded ends. The central area is narrow and linear. The valve face is flat. The valve face/mantle junction forms a sharp angle. The abvalvar edge of the mantle is parallel to the valve face/mantle junction. In girdle view, frustules are rectangular. Cells form short ribbon-like colonies, joined by linking spines. The axial area is linear. Striae are distinct, composed of round areolae. Areolae are uniform in size from axial area to valve mantle. Striae are parallel throughout the valve, and extend continuously onto the valve mantle, stopping shortly before the abvalvar mantle edge. Costae are wider than the striae. Spines are spatulate. Spines are present along the valve face edge, including the apices, and are located on the costae between striae. Well-developed, simple type, apical pore fields with round poroids are present. Pore fields are located on the junction between valve face and mantle. One rimoportula is present on each valve, located along a stria close to the axial area, expressed internally as a small labium. Copulae, or girdle bands, were not observed.


Frustules are linked by marginal spines to form colonies.

Original Description

F. virescens. Frustules broad, with two evident puncta at each end; lateral surfaces turgid-lanceolate, constricted near the ends; striae none, or indistinct. Frag. pectinalis, Ehrenb. Die. Infus. p. 206. t. 6. fig. 1; Ptrich. Infus. p. 222. fig. 176.

  • Basionym
    Fragilaria virescens
  • Author
    Ralfs 1843

Original Images

Original Description 3

EMAP Assessment

EMAP Distribution

Fragilariforma Virescens   Ralfs   Williams Et  Round 10
Map 10

Response Plots

Fragilariforma Virescens   Ralfs   Williams Et  Round

Cite This Page

Morales, E, and Spaulding, S. (2011). Fragilariforma virescens. In Diatoms of North America. Retrieved June 22, 2018, from https://diatoms.org/species/fragilariforma_virescens


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