• Category
  • Length Range
    18-33 µm
  • Width Range
    2.8-3.3 µm
  • Striae in 10 µm
    13-17 in the valve center, 18-22 at the ends, areolae unresolved in LM



The ventral margin is only slightly concave to nearly straight. The dorsal margin is convex. The apices are rostrate, dorsally deflected and set off by a change in slope of the dorsal margin. The helictoglossae are visible in the LM. The distal raphe ends curve dorsally. Striae are parallel. The areolae are unresolved in the LM.

Eunotia horstii valves are similar to E. gracillima valves (Lange-Bertalot et al. 1996, Plate 57: Figs 22 – 47) but E. horstii valves are broader and have denser striae. Eunotia horstii valves have similar measurements to E. groenlandica but the ends E. horstii valves are more recurved than those of E. groenlandica (Lange-Bertalot & Metzeltin 1996, Taf. 17: Figs 25 – 27; Lange-Bertalot & Genkal 1999, Taf. 6: Figs 3 – 9). Eunotia horstii is also similar to E. fallax but E. horstii has consistently spaced striae relative to E. fallax, especially in the central area of the valve.


To date, Eunotia horstii has been infrequently found from the bryophyte substrates in first and second order streams in the Great Smoky Mountains National Park

Original Description

Valves only slightly concave to nearly straight on ventral margin, convex on dorsal margin, with apices set off by a change in slope of the dorsal margin, 18 – 33 μm long, 2.8 – 3.3 μm wide. Apices rostrate, dorsally deflected. Helictoglossae visible in the light microscope. Rimoportula at one end of valve, at the center of the apex. Raphe with distal ends dorsally curved. Striae parallel, 13 – 17 in 10 μm in the valve center, 18 – 22 in 10 μm near the apices. Puncta unresolved in the light microscope.

  • Author
    Furey, Lowe and Johansen 2011
  • Length Range
    18-33 µm
  • Width
    2.8-3.3 µm
  • Striae in 10µm
    13-17 in the valve center, 18-22 at the ends, puncta unresolved in LM

Original Images

Eunotia horstii orig ilus
Eunotia Horstii Scannedtext

Cite This Page

Furey, P. (2011). Eunotia horstii. In Diatoms of North America. Retrieved June 21, 2024, from https://diatoms.org/species/eunotia_horstii


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