• Category
  • Length Range
    10–16 µm
  • Width Range
    2.5-4.0 µm
  • Striae in 10 µm
    20-25 in the center, 34-40 at the raphe valve ends; 20-28 in the center, 32-38 at the rapheless valve ends



Valves are linear-lanceolate with slightly drawn-out ends, often slightly asymmetrical about median transapical plane. Valves are 10-16 µm in length, and 2.5-4.0 µm wide. The raphe valve is concave. The raphe valve has a linear axial area, which widens slightly in the middle portion of the valve. This rectangular central area that reaches valve margin is often asymmetrical and may be termed a facia, or subfascia. Externally, the terminal raphe fissures are hooked towards the same side of the valve. Externally, the central raphe ends are teardrop-shaped and internally, curved to opposite sides. The rapheless valve is convex, with a narrow linear axial area widening slightly in the middle. The striae are parallel throughout both valves or very slightly radiate in the middle of the valve and slightly convergent at the apices. On the raphe valve, the striae density is 20-25 in 10 µm in the center and 34-40 in 10 µm at the apices. On the rapheless valve, the striae density is 20-28 in 10 µm in the center and 32-38 in 10 µm at the apices. External openings of areolae are transapically elongated or circular. Each stria in the center of the valve contains 2-4 areolae. The valve mantle bears one row of areolae.


Although formation of mucilaginous stalks was never observed in A. pyrenaicum, this species might be able to produce stalks as other Achnanthidium species.

Original Description

Schalen linear-lanzettlich mit stumpf gerundeten, oft leicht vorgezogen bis schwach kopfigen Enden, 7-10 µm lang, 3-4 µm breit, die kleinsten Individuen sind oft völlig elliptisch. Raphenlose Schalen mit sehr enger Pseudoraphe, Transapikalstreifen etwa 21 in 10 µm, senkrecht zur Mittellinie, nur an den äubersten Enden leicht radial, die Mittelstreifen jederseits der Pseudoraphe gewöhnlich etwas verkürtz. Raphenschale mit fadenförmiger raphe, Axialarea sehr eng, Zentralarea infolge der auch auf dieser Schale erfolgten Verkürzung der Mittelstreifen etwas quer verbreitert; Transapikalstreifen enger als auf der raphenlosen Schale, etwa 25 in 10 µm, durchweg leicht radial.

  • Basionym
    Achnanthes pyrenaica
  • Author
    Hust. 1966
  • Length Range
    7–20 µm
  • Width
    3–4 µm
  • Striae in 10µm
    25 in the center of raphe valve, 21 in the center of the rapheless valve

Original Images

 Achnanthes pyrenaica orig illus
Achnanthes pyrenaica  orig descr
Original text and images reproduced with permission by Teubner Verlag/GWV Fachverlage GmbH.

Cite This Page

Potapova, M. (2009). Achnanthidium pyrenaicum. In Diatoms of North America. Retrieved July 18, 2018, from https://diatoms.org/species/achnanthidium_pyrenaicum


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