• Category
  • Length Range
    9.0-11.9 µm
  • Width Range
    2.9-3.3 µm
  • Striae in 10 µm



Valves are linear to linear-elliptic with rounded ends, which are slightly drawn-out. Striae on both valves are biseriate. Areolae are elliptic or angular and transapically elongated. Internally, areoale are covered by hymenes. Striae are slightly radiate throughout both valves. Striae number 16-20 in 10 µm. Valve mantle bears one row of elongated areolae; one areola is opposite to a stria, and one is between two striae.

The raphe valve has narrow axial area, which widens into a small central area. Externally, the distal raphe ends are curved toward the same side of the valve. The distal raphe ends are slightly expanded. The central raphe ends are slightly expanded. Internally, the central raphe ends curve to opposite sides.

The rapheless valve has narrowly linear axial area, which sometimes widens unilaterally into a small central area.


reported from oligotrophic cold waters

Original Description

Schalen linear mit etwas erweiterter Mitte und schwasch kopfformigen stumpfen Enden. Lange 15-26 µm, Breite 5-6 µm, Querstreifen 14-17 in 0.01 µm, stark und deutlich punktiert, an der Unterschale etwas radial, an der Oberschale parallel und bisweilen in der Mitte fehlend.

  • Basionym
    Achnanthes nodosa
  • Author
    A.Cleve 1900
  • Length Range
    15-26 µm
  • Width
    5–7 µm
  • Striae in 10µm

Original Images

Achnanthes nodosa orig illus
Achnanthes nodosa  orig descr


Jun 23, 2024 - Achnanthes nodosa transferred to Rossithidium nodosum

Achnanthes nodosa was transferred to Rossithidium nodosum by Aboal in 2003. The transfer is now reflected in the website. Sarah Spaulding

Cite This Page

Potapova, M. (2009). Rossithidium nodosum. In Diatoms of North America. Retrieved June 23, 2024, from https://diatoms.org/species/rossithidium_nodosum


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