• Category
  • Length Range
    14-25 µm
  • Width Range
    4.1-5.3 µm
  • Striae in 10 µm
    15-20 in 10 µm in the center valve, 40-50 in 10 µm at the ends of raphe valve, 25-35 in 10 µm at the ends of rapheless valve



Valves are linear-lanceolate to lanceolate with subrostrate ends. 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. Externally, the central raphe ends are teardrop-shaped. Internally, the central raphe ends curve to opposite sides. The rapheless valve has a narrow, linear axial area, widening slightly in the middle. Striae are very 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 6-7 areolae. Very short marginal striae are often present in the middle portion of the valve.


Achnanthidium druartii has been reported in North America only recently from rivers in Kentucky and Virginia (Potapova, unpublished). This species is considered invasive in France (Rimet et al. 2010). It is not clear in either location, however, if the species was misidentified in the past and if it has a broader distribution.

Original Description

Valves lanceolate with slightly subrostrate ends never capitate. Valve length 12-29 μm (average 21 μm), valve width 3.9-5.8 μm (average 5 μm). Raphid valve is presenting proximal ends in the shape of tapered drops in external view which are distant by about 0.8 μm. Central endings in internal view are short and curved to opposite sides. The raphe sternum is larger in the middle of the valve than in the extremities. Rapheless valve is convex, with narrow straight sternum very slightly enlarged in the middle. Striae are very weakly radiate throughout on both valves. Occasionally there are short striae inserted near the middle of the valve. For both valves, stria density is 15-22 in 10 μm (average 18) at the valve center and about 40-50 in 10 μm near the apices. Striae in the middle part of the valve are composed of 6 to 7 areolae, whereas striae in the extremities are only composed of 3 to 4 areolae. External foramina of areola are round to slightly elongated. Internal foramina of areola are closed by a rectangular hymen. The internal foramina are forming lines inside a shallow depression and foramina are separated from each other except near the apex where they are coalescent. On both valves, the rows of areola are interrupted at the apex.

  • Author
    Rimet and Couté in Rimet et al. 2010
  • Length Range
    12-29 µm
  • Width
    3.9-5.8 µm
  • Striae in 10µm
    15-22 in the center valve, 40-50 at the ends

Original Images

Achnanthidium druarti orig illus
Achnanthidium druartii orig illus 2

Cite This Page

Potapova, M. (2011). Achnanthidium druartii. In Diatoms of North America. Retrieved July 24, 2024, from https://diatoms.org/species/achnanthidium_druartii


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