Valves are elongate, linear-lanceolate and dorsiventral. The apices are narrow and acute, slightly deflected toward ventral side in larger specimens. The raphe is lateral with external proximal ends that are slightly dorsally deflected before the distal ventral deflection. Internally, the raphe appears to be continuous through the central area. The distal raphe has relatively long terminal fissures, that is, the helictoglossae are distantly spaced from each valve apex. The axial area is linear and slightly expanded at the central area. A single isolated punctum is present on the dorsal side of the central area, in line with a central stria. The external expression of the punctum is small and circular, while the internal expression is elongate and opposite a bifurcate cleft in the intermissio. Striae are slightly radiate becoming convergent near the apices. This is most apparent on the ventral side of the valve as the stria density increases. Striae are uniseriate and composed of transapically elongated areolae.

The specimens shown here appear to align most closely with E. pergracile, although they are more narrow (6.5-7.8) than the specimens described by Krammer (1997).

This taxon is part of a large, diverse species complex (Krammer 1997). It includes both Cymbella gracilis (Ehrenberg) Kützing and C. gracilis (Rabenhorst) Cleve. It appears that the type of Cymbella gracilis is ambiguous, and that the name is poorly circumscribed. Further investigation may show additional North American species.


Encyonema pergracile was described from from Norway, but was also verified and illustrated from samples in Florida (Krammer 1997). It was found occasionally in rivers in the Sierra Nevada mountains of California (Spaulding, US Geological Survey, NAWQA survey 2012).

Original Description

  • Author
    Krammer 1997
  • Length Range
    27-57 µm
  • Width
    8-9.2 µm
  • Striae in 10µm

Original Images

Encyonema pergracile orig illus
Encyonema Pergracile Orig Des


Jul 22, 2018 - Correction of species name

This page originally appeared March 2, 2015 with the name Encyonema neogracile. These specimens appear to be more closely aligned with E. pergracile because of the length and width. These specimens, however, are smaller than E. pergracile (8-9.2) as given in the original description of Krammer (1997).

Cite This Page

Spaulding, S, and Bishop, I. (2014). Encyonema pergracile. In Diatoms of North America. Retrieved July 22, 2018, from


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