• Category
  • Length Range
    12.8-25.6 µm
  • Width Range
    1.8-2.2 µm
  • Striae in 10 µm



Valves are small, narrow and linear to linear-lanceolate, tapering to narrow rostrate apices. The axial area is broadly lanceolate. Striae are short, marginal, alternating and slightly radiate. The central area is variable, with striae slightly shortened on one side and absent on one side, or absent on both sides. The absence of striae makes the central area appear hyaline when viewed with the light microscope, but when enlarged and enhanced in photographs the central area may appear to have ghost striae.


Morales (2003) noted that Fragilaria pennsylvanica likely forms sessile stellate colonies. The Pennsylvania streams in which it has been found so far are non-calcareous and have relatively warm temperatures (21-27°C) during the growing season (Morales 2003).

Original Description

Length: 12–24.5 μm, width: 1–2.5 μm, striae: 18–22 per 10 μm. Central area clear on one or both sides (Figs. 20, 22). Central sternum wide and lanceolate (Figs. 20–26). Striae alternate and short, composed of round to slightly apically elongated areolae. Up to four areolae located on valve face and up to two on the valve mantle per stria. Volae were not observed. Spines absent. Apical pore fields of the ocellulimbus type with three to four rows of vertical poroids (Figs. 25–26). One rimoportula present (Figs. 24, 25). Girdle bands closed apparently bearing small isolated unoccluded perforations (Figs. 27–29). Plastids unknown.

  • Author
    E.Morales 2003
  • Length Range
    12-24.5 µm
  • Width
    1-2.5 µm
  • Striae in 10µm

Original Images

Fragilaria pennsylvanica orig illus
Fragilaria Pennsylvanica  Morales Originaldescription

Cite This Page

LaLiberte, G. (2015). Fragilaria pennsylvanica. In Diatoms of North America. Retrieved May 29, 2024, from https://diatoms.org/species/fragilaria_pennsylvanica


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