• Category
  • Length Range
    13.5-20 µm
  • Width Range
    3.2-4.2 µm
  • Striae in 10 µm
  • Reported As
    Eunotia paratridentula (Kulikovsky and Lange-Bertalot 2011, pg. 33, Pl. 19, Fig. 1-9, Pl. 37, Fig. 3-6 )
    Eunotia perpusilla var. perpusilla (Patrick 1958, pg. 7, Pl. 1, Fig. 7)



Valves are dorsiventral. The ventral margin is concave, with two subapical swellings. The dorsal margin is convex and undulate, with the number of undulations varying with valve size (typically 3-4). Striae are radiate, evenly spaced, with occasional shortened striae intruding from the dorsal margin. Apices are protracted, capitate and weakly recurved. Terminal raphe ends are distinct in LM and positioned near the ventral margin.

Additional nomenclatural observations

In Van Heurck’s Atlas (1880-1881), a drawing with the caption “E. tridentula Ehr. var.? perpusilla Grun.” was published. In the “Table Alphabetique” (the accompanying text for the Atlas plates), which was published in 1884, Van Heurck changes his mind and drops the “var.? perpusilla”, leaving “E. tridentula Ehr.” and still referring to the same figure in the Atlas (Pl. XXXIV, Fig. 31).

In 1939, A. Berg elevated E. tridentula var. perpusilla to the rank of species, resulting in Eunotia perpusilla (Grunow) Berg. While he did not specifically include the text “stat. nov.”, at the time this was not required of him and the omission does not invalidate his transfer.

It is the author’s opinion that E. muscicola var. tridentula Nörpel & Lange-Bertalot 1993 (and its current form Eunotia paratridentula Lange-Bertalot & Kulikovsky 2011) is conspecific with E. perpusilla (Grunow) Berg, as illustrated in Van Heurck’s Atlas.

It should be noted that Lange-Bertalot has a separate interpretation of the identity of E. perpusilla. He believes that E. perpusilla (referring to its basionym E. tridentula var. perpusilla) is synonymous with E. microcephala Krasske ex Hustedt 1932, and we believe this to be incorrect (Lange-Bertalot et al. 2011). Lange-Bertalot and Nörpel also considered Eunotia perpusilla Grunow sensu Patrick 1958 to be conspecific with E. muscicola var. tridentula (Krammer and Lange-Bertalot 1991). Lastly, it should also be noted that Patrick referred to North American specimens, such a those above, as E. perpusilla. Unfortunately, she attributed the incorrect authority, using Grunow, instead of (Grunow) Berg (Patrick 1958).


This taxon is frequently found in the temperate holoarctic (Kulikovsky et al. 2011). In recent USGS NAWQA surveys, E. perpusilla has been confirmed in the Pacific Northwest (Puget Sound basin and Willamette Valley) and across the eastern US, from western Maine to northern Georgia. Patrick (1958; 1966) found it in western Montana (Missoula and Ravalli counties). Although broadly distributed, relatively few valves are reported in these North American localities.

Original Description

  • Basionym
    Eunotia tridentula var. perpusilla
  • Author
    Grunow 1881

Original Images

Eunotia tridentula var. perpusilla orig illus

Cite This Page

Bishop, I. (2017). Eunotia perpusilla. In Diatoms of North America. Retrieved July 22, 2018, from https://diatoms.org/species/eunotia_paratridentula


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