• Category
  • Length Range
    39 – 77 µm
  • Width Range
    10.5-13.5 µm
  • Striae in 10 µm
  • Synonyms
    Epithemia argus var. alpestris (W.Sm.) Grunow
    Cystopleura argus var. alpestris (W.Sm.) De Toni
    Cystopleura argus var. alpestris (W.Sm.) Gutw. 1899
  • Reported As
    Epithemia argus (Schmidt et al. 1904, Pl 251, fig 12-13)
    Epithemia argus (Wornardt 1964, Pl 2, fig 12)



Valves are dorsiventral with protracted and slightly reflexed ends. The dorsal margin of the valve is convex and the ventral margin is slightly concave. The costae are slightly radiate with an average of 2-3 costae in 10 µm. The striae are coarse, 10-12.5 in 10 µm, and have distinct areolae. There are often 4 striae between costae, but, due to the irregular spread of the costae, there can be a range of 2-6 striae between costae. The proximal raphe ends curve to a point that ends closer to the dorsal side than to the ventral side. At the central arch of the raphe, the top edge of the raphe terminates 2.8-4.6 µm from the dorsal edge, and the bottom edge of the raphe is 5.6-7.6 µm from the ventral side. The distal raphe ends are dorsally curved and terminate near the center of the valve apices. Between the proximal and distal areas, the raphe lies visibly along the ventral margin. Among individuals of the same species, there is some variation in the width of the costae, amount of reflection in the apices, and relative length to width ratio of the valves (Length:width in the studied populations was 3.7-6.5).

The treatment of E. argus var. alpestris in Patrick and Reimer (1975), differs significantly from Smith’s original image and description. The figure in Patrick and Reimer (1975) has a less arched dorsal margin, more rostrate and less reflexed apices, and much less apparent distal raphe ends. The populations observed in this study align more with Smith’s original description in that the proximal raphe ends are more ventral, the valves have narrower widths, and the valves have a narrower range in lengths.

The holotype illustration of Epithemia argus in Schmidt et al. (1904) has reflexed ends. On the same plate, however, Figs 2, 3, and 9 are named E. argus var. alpestris, but possess rounded ends.


Epithemia alpestris was found in a muddy pool formed by a spring running down a mound at Silver Lake Fen, Dickinson County, Iowa in July of 2017. At the time of collection, pH was 7.13, temperature was 19.8 °C, and conductivity was 707 ppm. All specimen observed had degraded, scenescent chloroplasts.

Though E. alpestris was not reported previously in the Iowa Lakeside Lab Herbarium, specimens were found a slide from Excelsior Fen, as well as a moss squeeze sample taken from Silver Lake Fen. This taxon is likely to occur in many other fen-type areas, since E. alpestris is typically associated with spring fed streams and marshes with higher electrolyte concentrations (Krammer and Lange-Bertalot, 1988).

The type locality of E. alpestris is Katefield near Lancaster, England (Smith 1853). Verifiable distribution of E. alpestris includes Füssen, Mooswiese (Krammer and Lange-Bertalot, 1988). Epithemia alpestris has also been found, but reported as E. argus, in Loch Kinord, Aberdeenshire, Scottland (Schmidt, 1903) and in fossil material from the Pleistocene in Panamint Valley, California (Wornardt 1964).

Live Valve View
Dying Epithemia alpestris in valve view. This is the same individual that is shown in the live girdle view image.
Live Girdle View
Dying Epithemia alpestris in girdle view. This is the same individual that is shown in the live girdle view image. E. alpestris was more commonly found in girdle view than valve view in live samples..
Sample Site
Credit: Image taken by Shelly Wu
Sample site at Silver Lake Fen

Original Description

Epithemia alpestris, w. sm. F. V. linear; V. recurved at the obtuse extremities ; foramina large ; striae 27 in .001”. v.s.

Kütz. Bacill. V. 16? Fresh water. Katefield near Lancaster, Mr. G. Smith, April 1851. Plate I. 7.

  • Author
    W.Sm. 1853

Original Images

E alpestris orig illus
E Alpistris Orig Des

Cite This Page

Drahos, A. (2017). Epithemia alpestris. In Diatoms of North America. Retrieved August 26, 2019, from https://diatoms.org/species/epithemia_alpestris


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