• Category
  • Length Range
    12-21 µm
  • Width Range
    3.0-3.7 µm
  • Striae in 10 µm
    21-25 in the center valve, 36-45 at the valve ends
  • Synonyms
    Achnanthes altergracillima Lange-Bert.



Valves are linear-lanceolate with narrowly rostrate to subcapitate ends. The raphe valve is concave and the rapheless valve is convex. Both valves possess a linear axial area, which widens slightly in the middle portion of the valve. No central area is present. The striae are parallel or slightly radiate throughout both valves. The external openings of the areolae are transapically elongated, appearing as narrow slits. Each stria in the middle part of the valve is composed of 4-5 areolae. Short marginal striae are often present in the middle portion of both valves. The raphe is straight, filiform. The terminal raphe fissures are sharply bent. Externally, the central raphe ends are teardrop-shaped. Internally, the central raphe ends curve to opposite sides.


Original Description

Schalen linear-lanzettlich mit gerundeten, breiten Enden, 25-40 μ lang, 3-4 μ breit. Streifen parallel, etwa 30 in 10 μ; Unterschale mit kleinem Mittelfeld.

  • Basionym
    Microneis gracillima
  • Author
    Meister 1912
  • Length Range
    25-40 µm
  • Width
    3-4 µm
  • Striae in 10µm

Original Images

Or Ill001
Or Descr

Cite This Page

Potapova, M. (2010). Achnanthidium gracillimum. In Diatoms of North America. Retrieved May 30, 2024, from https://diatoms.org/species/achnanthidium_gracillimum


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