• Category
  • Length Range
    16.4-25.7 µm
  • Width Range
    4.7-6.1 µm
  • Striae in 10 µm
  • Reported As
    Fragilariforma strangulata (ANSP Image Database (IM000867))
    Fragilaria virescens var. torus (Desianti et al. 2015, pg. 108, Fig. 127)



Valves are linear, becoming lanceolate at in smaller specimens. Apices are protracted and strongly capitate. A single rimportula is present at one apex. Striae are unevenly spaced, alternate, parallel throughout most of the valve and become curved at the apices. The sternum is very narrow and occasionally not present. No spines are visible in LM. Areolae are dense and also not visible in LM.

This taxon has been misidentified in surveys as Fragilariforma strangulata, a species described from the Belgian Congo.

Note that Fragilaria virescens var. torus Hohn and Hellerman 1966 is a heterotypic synonym of Fragilariforma marylandica (Desianti et al. 2015). Note that while F. marylandica was published later than Fragilaria virescens var. torus, it was published at the rank of species (rather than variety).


This taxon was found in two small, humic acid lakes in the Pinelands of New Jersey and in a tributary of the Severn River in Maryland (Siver and Hamilton 2011). The type population was collected from epipsammic and epilithic habitats. The imaged populations on this page were collected in the northeast, in the East Branch of the Neversink River, New York and Bearcamp River, New Hampshire.

Original Description

  • Author
    Edlund, Laub, Siver, Hamilton and E.Morales 2011

Original Images

Fragilaria marylandica orig illus
Fragilaria marylandica orig illus 2
F Marylandica Orig Desc Text

Cite This Page

Bishop, I. (2016). Fragilariforma marylandica. In Diatoms of North America. Retrieved July 22, 2018, from https://diatoms.org/species/fragilariforma_marylandica


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