• Category
  • Length Range
    37-72 µm
  • Width Range
    16-23 µm
  • Striae in 10 µm
    dorsal side: 8-10 center, 11-12 ends; ventral side: 9-12 center, 12-14 ends
  • Synonyms
    Cymbella triangulum (Ehrenb.) Cleve 1894
  • Reported As
    Cymbella triangulum (Patrick & Reimer 1975)



Valves are elliptic-lanceolate and moderately asymmetric to the apical axis, with smoothly convex dorsal and ventral margins. The apices are and acute and apiculate. The axial area is variable in width, 3-6 times wider than the raphe. The central area is only slightly wider than the axial area. The raphe is lateral and arched, becoming concave toward the dorsal side. Proximal raphe ends are slightly expanded and deflected dorsally; distal raphe ends are recurved ventrally. Striae are slightly radiate, becoming parallel and then convergent at the apices, especially on the ventral side. The central one or two striae on the dorsal side are often slightly longer than adjacent striae. Areolae are very coarse and number 8-10 in 10 µm.


Encyonema triangulum is widely distributed in hardwater streams and lakes throughout the United States (Patrick & Reimer 1975). There are 39 records of this species in the Montana Diatom Collection from the Northwestern United States. Here the mean pH is 7.4 and the mean specific conductance is 2261 μS/cm (see table below for other variables). Common diatom associates of E. triangulum are Navicula subrhynchocephala, Navicula namibica, Navicula germainii, Nitzschia sigma, Plagiotropis lepidoptera var. proboscidea, Tryblionella gracilis, and Navicula amphiceropsis.

Lake  Metigoshe2
Credit: Loren Bahls
School Section Lake, Lake Metigoshe State Park, Bottineau County, North Dakota: home of Encyonema triangulum.
Encytriangulum Chem
Credit: Montana Diatom Database
Abundance-weighted means for selected water quality variables measured concurrently with the collection of samples that contain Encyonema triangulum.

Original Description

GLOEONEMA? triangulum: Gl. corpusculis naviculaceis utrinque acutis, dorsi gibbere altiore inaequalibus et in formam a latere conspicuam triangularem abeuntibus. Diam. Naviculae 1/66'''. Vivum in Niagara. Tubulos continuos non vidi, sed Gloeonemati paradoxo associatum vidi, cujus tubuli aderant cum singnlis eodem modo sparsis corpusculis.

  • Basionym
    Gloeonema triangulum
  • Author
    Ehrenb. 1845

Original Images

Encyonema Triangulum  Orig Descr

Cite This Page

Bahls, L. (2012). Encyonema triangulum. In Diatoms of North America. Retrieved June 13, 2024, from https://diatoms.org/species/encyonema_triangulum


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