• Category
  • Length Range
    28.1-61.3 µm
  • Width Range
    5.8-8.3 µm
  • Striae in 10 µm
  • Reported As
    Frustulia spicula var. alpina (Amossé 1972, p. 307, figs 23:2-6)



Valves are linear, sometimes with undulate or slightly concave margins. The apices are rostrate to subrostrate. The central area is linear and elongate. Raphe branches are distinctly curved and bordered by longitudinal ribs that do not extend into the central area. Proximal ends of the longitudinal ribs are blunt; distal ends are narrow and indistinct. Striae are parallel at the valve center, slightly convergent towards the ends, and radiate around the apices. Areolae number 28-32 in 10 μm.


There are four records of F. amosseana in the Montana Diatom Collection, two from streams, and one each from a fen and a pond. All of these waters are along the Rocky Mountain Front in north-central Montana and southwestern Alberta, Canada. The largest population was found in Pine Butte Fen (photos below). Pine Butte Fen is fed by the headwaters of the Teton River, which drain a region of limestone geology in the Bob Marshall Wilderness. Ross and Sims (1978) report this species from several waters in the U.K. with alkaline pH and moderate conductivity. Lange-Bertalot (2001) considers this species to be cosmopolitan, but infrequent, particularly in intermittent alkaline waters with higher electrolyte content.

Pine  Butte
Credit: Loren Bahls
Pine Butte Fen, Teton County, Montana, home of Frustulia amosseana. This view is looking east from the Rocky Mountain Front towards Pine Butte.
Ear  Mountain001
Credit: Loren Bahls
Pine Butte Fen looking west from the top of Pine Butte towards Ear Mountain on the Rocky Mountain Front.

Original Description

Valve broadly linear, or with slightly concave margins, tapering towards the broad or slightly subcapitate obtuse apices, mantle shallow, 27-48 µm long, 5-6.5 µm broad. Central and axial areas forming a linear space, appearing slightly constricted at some levels of focus, and slightly narrowed towards the elliptical and slightly widened terminal areas. Striae parallel in the central part of the valve, slightly convergent in the distal parts, and radiating around the terminal nodules, about 30 in 10 µm; areolae about 30 in 10 µm, in irregular longitudinal rows that tend to be concave towards the branches of the raphe. Outer fissures of the raphe slightly reflexed at the centre and the apices, slightly widened at the centre to form a central pore on either side of which is a minute depression in the valve surface. Central nodule elongate-elliptic, occupying about half the width of the central area.

  • Basionym
    Berkella linearis
  • Author
    R.Ross and P.A.Sims 1978
  • Length Range
    27-48 µm
  • Width
    5-6.5 µm
  • Striae in 10µm
    about 30

Original Images

Berkella linearis orig illus
Berkella linearis orig descr

Cite This Page

Bahls, L. (2016). Frustulia amosseana. In Diatoms of North America. Retrieved June 23, 2024, from https://diatoms.org/species/frustulia_amosseana


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