• Category
  • Length Range
    9-14 µm
  • Width Range
    2.9-4.0 µm
  • Striae in 10 µm
  • Synonyms
    Achnanthes subhudsonis var. kraeuselii (Cholnoky) Cholnoky 1956
  • Reported As
    Achnanthes subhudsonis (Hustedt 1921, p. 144; fig. 9-12)
    Achnanthidium subhudsonis (Kobayasi et al. 2006, p. 13, 129)



Valves are narrow and lanceolate. The raphe valve has a lanceolate axial area becoming narrow at the apices. The raphe is expanded near the valve center and the external proximal raphe ends have expanded pores. Internally, the proximal raphe ends are slighly deflected to the opposite side from the terminal fissures. The terminal raphe fissures are deflected to the same side and extend over the valve mantle. Striae are radiate and more broadly spaced at the central valve than near the ends. The rapheless valve is flexed about the apical axis. The rapheless valve also has a more narrow lanceolate axial area than the raphe valve. The axial area of the rapheless valve is asymmetrically bent near the apices in many specimens. Striae are slightly radiate on the rapheless valve. The striae are composed of poroid areolae. The external and internal openings of the areolae are circular, or nearly so.

Note that Hustedt (1921) described the species, A. subhudsonis from tropical regions. This taxon is reported as having a higher stria density and parallel striae (as compared to radiate striae)(Simonsen 1987) than the specimens illustrated here. Cholnoky (1954) described A. kraeuselli and later included it as a variety, A. subhudsonis var. kraeuselii, the name we adopt here. We expect that future work with resolve the differences, if there are differences, between the nominate and other varieties. We also expect that this taxon will soon be included in a new genus; it is clearly not aligned with either Achnanthes as it was originally described (Cholnoky 1954), or Achnanthidium as it was later transferred (Kobayashi et al. 2006).


Achnanthes subhudsonis var. kraeuselii was described from moss and aerophilic habitats in South Africa (Cholnoky 1954). This tropical species is considered to be an invasive species to Europe (Hofmann et al. 2011). It is not clear if it is also a new arrival to North America.

Original Description

  • Basionym
    Achnanthes kraeuselii
  • Author
    Cholnoky 1954
  • Length Range
    12-25 µm
  • Width
    4-6 µm
  • Striae in 10µm

Original Images

Achnanthes kraeuselii orig illus
Achnanthes kraeuselii orig descr


Oct 03, 2018 - Transfer from Achnanthes to Achnanthidium

Previous to October 3, 2018, this taxon appeared as Achnanthes subhudsonis var. kraeuselii (Cholnoky) Cholnoky 1956. The page was updated following Kusber et al. (2017). - S. Spaulding

Cite This Page

Spaulding, S., Potapova, M. (2014). Achnanthidium subhudsonis var. kraeuselii. In Diatoms of North America. Retrieved July 13, 2024, from https://diatoms.org/species/achnanthidium_subhudsonis_var._kraeuselii


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