• Category
  • Length Range
    22.1-37.5 µm
  • Width Range
    9.1-10.5 µm
  • Striae in 10 µm



Large valves are lanceolate with tri-undulate margins, smaller valves are rhombic-lanceolate. Central undulation is the widest part of the valve and the apical undulations are more pronounced in larger specimens. Apices are broadly tapered, with rounded apices. A narrow sternum is present. Striae are parallel at the valve center, becoming radiate and slightly curved toward the apices.

Kingston et al. (2001) neotypified Fragilariforma polygonata using Newfoundland material after extensive search of Cleve-Euler's (1953) syntypes showed no valves of "Fragilaria polygonata" present. The concept presented here follows Kingston et al. (2001).


Fragilaria polygonata is reported from dystrophic New England lakes (Kingston et al. 2001) south to North Carolina (Siver and Hamilton 2011). Specimens illustrated here are from a boreal river in northern Minnesota in waters high in dissolved organic carbon and from a sediment core collected in an 8-m deep oligo- to mesotrophic lake (Shoepack Lake) located in Voyageurs National Park.

Frpolygonata  Usgsbiodata
Credit: USGS/Biodata
The distribution of F. polygonata in rivers of the United States. Accessed on 17 July, 2017.

Original Description

F. polygonata n. sp. Schalen linear-lanzettlich mit einer mittleren, beiderseitig rechtwinklig u. keilig zugespitzten Ausstülpung, an beiden Seiten der Ausstülpung meistens leicht eingeschnürt. Enden entweder keilig verdünnt, stumpf gestutzt, oder apikulat, in eine schmale Spitze auslaufend. Pseudoraphe nicht hervortretend, Str. parallel u. fein, etwa 20 auf 10 µ. L. 32-34 µ. Br. 8,5-10 µ (Mitte), in den Einschnürungen 4,5-5,5 µ.

  • Basionym
    Fragilaria polygonata
  • Author
    A.Cleve 1953
  • Length Range
    32-34 µm
  • Width
    8.5-10 µm
  • Striae in 10µm

Original Images

Frag Polygonata Type
Frag Polygonata Descriptoin


Jan 09, 2024 - Addition of Autecology

From 2017 until January 2024 the autecological information on this taxon page was limited. As of this update, information on ecology, biogeography, and environmental optima have been added. The size range was also expanded. - Mark Edlund

Cite This Page

Burge, D., Edlund, M., Allen, L. (2017). Fragilariforma polygonata. In Diatoms of North America. Retrieved May 18, 2024, from https://diatoms.org/species/fragilariforma_polygonata


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