• Category
  • Length Range
    7.4-28.3 µm
  • Width Range
    3.1-5.3 µm
  • Striae in 10 µm
    15-28 in the middle of raphe valve



Valves are linear-elliptica to elliptic, with subrostrate ends. The raphe valve is concave. The raphe valve possesses a linear axial area, which widens slightly in the middle portion of the valve. The terminal raphe fissures are hooked towards the same side of the valve and are slightly expanded at the ends. Externally, the proximal raphe ends are teardrop-shaped. Internally, the proximal raphe ends curve to opposite sides. The rapheless valve is convex. It has a narrow, linear axial area widening slightly in the middle. Striae are parallel or very slightly radiate throughout both valves. Stria density of the raphe valve is 15-28 in 10 µm in the middle and 35-50 in 10 µm at the apices. Stria density of the rapheless valve is 15-26 in 10 µm in the middle and 30-35 in 10 µm at the apices. 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. Very short marginal striae are often present in the middle portion of the valve.

Note that the great range in stria density within these observations, as well as within the original description, is due to the strong gradient of change in stria density particularly at the ends of the valves. Furthermore, the density depends on the length measured. For example, the number of striae in 10 µm, 5 µm or 2 µm (measured in SEM images) will each result in a different measure.

Original Description

Valve linear-elliptical to elliptical with extremities varying from subtlely protracted subrostrate to obtusely rounded, not protracted. Raphe valve with narrow, linear axial area curving at the ends; central area small, elongate-elliptical or lacking. Raphe filiform; proximal raphe ends close; distal ends curved or deflected in the same direction, subterminal. Striae parallel or very slightly radiate. Indistinctly punctate; more distant at the center of the valve than at the ends. Pseudoraphe valve with narrow, linear pseudoraphe; no distinct central area. Striae parallel or slightly radiate; indistinctly punctate. Striae, 20-22 in 10 µm at the center, becoming about 28-30 in 10 µm near the ends on both valves. Length, 7-25 µm. Breadth, 3.8-4.5 µm.

  • Basionym
    Achnanthes deflexa
  • Author
    Reimer 1966
  • Length Range
    7-25 µm
  • Width
    3.8-4.5 µm
  • Striae in 10µm
    20-22 in the center valve, 28-30 at the ends

Original Images

Achnanthes deflexa orig illus
Achnanthes deflexa orig illus 2
Achnanthes deflexa orig descr
Original text and images reproduced with permission by Academy of Natural Sciences of Philadelphia.

Cite This Page

Potapova, M. (2009). Achnanthidium deflexum. In Diatoms of North America. Retrieved May 30, 2024, from https://diatoms.org/species/achnanthidium_deflexum


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