• Category
  • Length Range
    17.8-28.0 µm
  • Width Range
    6.4-7.5 µm
  • Striae in 10 µm
  • Reported As
    Cymbella obscura (Krammer and Lange-Bertalot 1986, p. 306, figs 119:17-20)
    Encyonema obscurum (Krammer 1997, p. 107, figs 28:1-8, 29:1-13, 30:1-15, 31:1,2, 33:1-5,14-20)
    Encyonema drakei (Bahls 2014, p. 67, figs 31-39)



Valves are strongly dorsiventral with rostrate to subcapitate apices. Apices are oriented almost laterally such that the junction between the dorsal margin and the apex is concave. The dorsal margin is strongly arched. The ventral margin is slightly convex. The axial area is very narrow. The central area is a slightly wider continuation of the axial area. The raphe is filiform. Proximal raphe ends are deflected dorsally and terminate with slightly inflated central pores. Terminal raphe fissures are deflected ventrally. Striae are radiate on the dorsal side, a bit farther apart at the valve center than toward the apices. The median stria on the dorsal side meets the central area with a single isolated areola. The very short striae on the ventral side are radiate, then parallel, and finally convergent at the apices. Areolae in the striae are very fine and difficult to resolve in LM.


This taxon was described from material collected in Spitsbergen, Norway. Krammer and Lange-Bertalot (1986) report it as a "nordic-alpine" species found in lakes of subalpine regions and the Lower Alps. The specimens shown on this web page were collected from Lake Josephine, a subalpine lake in Glacier National Park, Montana. At the time of collection, pH in Lake Josephine measured 7.59 and specific conductance was 94 µS/cm.

Another population of Encyonema obscurum, possibly an ecomorph, was collected from a pond in the North Cascade Mountains of Washington (see photos below). This population was described and reported as Encyonema drakei by Bahls (2014).

L  Josephine
Credit: Loren Bahls
Lake Josephine, Glacier National Park, Montana: home of Encyonema ventricosum
Encyonema Obscurum North Cascades
Credit: Loren Bahls
A population (ecomorph?) of Encyonema obscurum from a pond in the North Cascade Mountains of Washington, reported as Encyonema drakei.
Boundary Trail Pond3A
Credit: Ryan Davis, Adventurers and Scientists for Conservation
Boundary Trail Pond #3, Okanogan County, Washington.

Original Description

  • Basionym
    Cymbella obscura
  • Author
    Krasske 1938
  • Length Range
    24-27 µm
  • Width
    7.0-7.5 µm
  • Striae in 10µm

Original Images

Encyonema obscurum orig illus 2
Encyonema Obscurum Origimag001

Cite This Page

Bahls, L. (2016). Encyonema obscurum. In Diatoms of North America. Retrieved June 19, 2024, from https://diatoms.org/species/encyonema_obscurum


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