• Category
  • Length Range
    15.1-19.8 µm
  • Width Range
    6.4-7.2 µm
  • Striae in 10 µm
    30-32 near the center of the raphe valve, 24-28 near the center of the rapheless valve
  • Reported As
    Stauroneis recondita (Krasske 1937, p. 41, pl. 26, fig. 32)
  • Genus Considered



Valves are linear-elliptic with narrow subcapitate apices. The raphe valve has a very narrow axial area that widens abruptly into a transverse fascia. The fascia is shaped like a bow tie and sometimes bordered by a few shortened striae. On the rapheless valve, the axial area is wider and expands gradually to merge with an asymmetric, irregular transverse central area. The raphe is straight. The terminal fissures appear to curve in opposite directions. The proximal raphe ends are expanded in the shape of tear drops. Striae on the rapheless valve are nearly parallel at the valve center but otherwise radiate, more so near the apices. Striae on the rapheless valve are also more closely spaced near the apices. Striae on the raphe valve are strongly radiate throughout and a bit more closely spaced near the apices.

Cleve-Euler (1953) amended her original description to confirm the presence of a fascia and to give more a accurate stria count: 24 in 10 µm on the rapheless valve and about 30 in 10 µm on the raphe valve. In LM, this taxon is morphologically similar to Achnanthidium exiguum and should probably be transferred to Achnanthidium.


This is a northern species found in cold, oligotrophic waters. It was described from Finnish Lapland (Cleve-Euler 1934) and later reported from Iceland (Foged 1974). The specimens illustrated here were collected from four small lakes in the Rocky Mountains of Montana, near the Canadian border. Three of these lakes are in Glacier National Park. In these four lakes electrical conductance ranges from 30 to 250 µS/cm and pH ranges from 7.2 to 7.8.

Johns  Lake  Gnp  Hikespeak Com
Credit: Hikespeak.com
Johns Lake, Glacier National Park, Montana: home of A. rostellata

Original Description

  • Author
    Cleve-Euler 1934
  • Length Range
    17 µm
  • Width
    6-6.5 µm
  • Striae in 10µm
    21-22 on the raphe valve, about 19 on the rapheless valve

Original Images

Achnanthes rostellata orig illus
Achnanthes rostellata orig descr

Cite This Page

Bahls, L. (2016). Achnanthes rostellata. In Diatoms of North America. Retrieved July 21, 2018, from https://diatoms.org/species/achnanthes_rostellata


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