• Category
  • Length Range
    24-32 µm
  • Width Range
    4.8-6.5 µm
  • Striae in 10 µm
    18-20 at the valve center, 21-23 at the apices



Valves are linear to linear-lanceolate and subtly triundulate. Valves are nearly symmetric with respect to the apical axis. Apices are capitate. The axial area is narrow and the central area is small and asymmetric, typically rounded on the dorsal side and squared on the ventral side. The raphe is lateral with proximal ends deflected to the dorsal side and ventral ends hooked toward the ventral side. Striae are radiate throughout and a bit more closely spaced near the apices. Areolae are very fine and difficult to resolve in LM.


Encyonopsis dakotae is known from the type locality, the Cheyenne River in Fall River County, South Dakota, and from Connelly Fen, a calcareous fen in Glacier County, Montana (photo below). Water quality data are not available for the type locality. The pH of Connelly Fen was 7.4 and specific conductance measured 1600 µS/cm.

Connelly  Fen  Site 1
Credit: Peter Lesica
Connelly Fen, Blackfeet Reservation, Glacier County, Montana: home of Brachysira vitrea.

Original Description

Valves linear-lanceolate and slightly dorsiventral. Apices capitate. Valve length 24–32 µm; valve width 4.8–6.5 µm. Axial area narrow, close to valve midline. Central area transverse, asymmetric, rounded on the dorsal side, defined by two or three irregularly shortened striae on the ventral side. Raphe weakly lateral, filiform near the proximal and distal ends. Proximal raphe ends weakly expanded, deflected dorsally. Distal raphe fissures hooked toward the ventral side. Striae radiate throughout, 18–20 in 10 µm at valve center, 21–23 in 10 µm near the apices.

  • Author
    Bahls 2013
  • Length Range
    24-32 µm
  • Width
    4.8-6.5 µm
  • Striae in 10µm
    18-20 at valve center, 21-23 near the apices

Original Images

Encyonopsis dakotae orig illus
Encyo Dakotae Origdesc001

Cite This Page

Bahls, L. (2013). Encyonopsis dakotae. In Diatoms of North America. Retrieved May 30, 2024, from https://diatoms.org/species/encyonopsis_dakotae


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