• Category
  • Length Range
    82-110 µm
  • Width Range
    23-26 µm
  • Striae in 10 µm
  • Reported As
    Neidium kozlowii (Krammer and Lange-Bertalot 1986, p. 276, fig. 102: 12-13)



Valves are elliptic-lanceolate with gradually protracted, relatively narrow subrostrate apices. A longitudinal line is evident along each margin. The axial area is rather broad and includes a row of irregularly spaced areolae along one side of both raphe branches. The central area is rectangular and positioned diagonally to the valve midline. Short striae, composed of areolae of irregular size and spacing, occur along both margins of the central area. The raphe is lateral, becoming filiform at the proximal ends. The proximal raphe ends are deflected sharply in opposite directions. The distal raphe fissures are bifurcate. Striae near the valve center are arranged diagonally with respect to the valve midline and become convergent towards the apices.


In addition to the type locality, Neidium undulatum was collected from Grassy Lake in the Axolotl Lakes near Ennis, Montana, elevation 2290 m. On the date the Grassy Lake sample was collected (29 September 2011), pH measured 9.73 and specific conductance measured 177 µS/cm.

Grassy  Lake 1
Credit: Loren Bahls
Grassy Lake in the Axolotl Lakes near Ennis, Madison County, Montana: home of Neidium undulatum.

Original Description

Valves long elliptic-lanceolate with triundulate margins and rather long broadly rounded sub-rostrate ends. Striae diagonal to midline of valve, having tendency to radiate in central portion of valve and to become parallel or slightly convergent at ends. Striae distinctly punctate. Axial area fairly broad, slightly diagonal, to perapical axis. Central area rectangular, distinctly diagonal, at margins of valve not sharply defined due to irregularity of striae. Both axial and central areas often have scattered punctae of somewhat abnormal appearance. Raphe generally linear, often appearing undulate due to contour of valve. Proximal raphe hooks short, attenuate, distal raphe ends narrowly bifurcate.

  • Basionym
    Neidium kozlowi var. undulata
  • Author
    Stoermer 1963
  • Length Range
    98 µm
  • Width
    24 µm
  • Striae in 10µm

Original Images

Neidiumokobojii Origimag
Neidiumokobojii Origdesc

Cite This Page

Bahls, L. (2013). Neidium undulatum. In Diatoms of North America. Retrieved April 16, 2024, from https://diatoms.org/species/neidium_undulatum


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