• Category
  • Length Range
    10-23 µm
  • Width Range
    6.0-9.6 µm
  • Striae in 10 µm
    10-12 at the valve center
  • Synonyms
    Navicula cascadensis Sovereign 1960



Valves are elliptic with cuneate apices. The raphe is straight and filiform with slightly expanded proximal ends. The axial area is narrow and linear. The central area is small and elliptic, and a small stigma appears to be present. Striae are uniseriate and radiate. Striae at the center of the valve are more widely spaced than striae near the apices. The round to apically elongate areolae are coarse, visible under LM, and number 28-36 in 10 µm. Two to four pairs of annulae are present at the apices.

With two to four pairs of annulae at each apex, this taxon clearly belongs in the genus Geissleria and should be considered for nomenclatural transfer. This taxon differs from other species of Geissleria in North America by the coarse areolae. SEM examination is needed to confirm the presence of a stigma.


This taxon is endemic to the Cascade Mountains of western Oregon. Here it lives in lakes and streams with low electric conductivity (24-38 µS/cm) and slightly acid pH (6.70-6.93).

Orsnw1010 219
Credit: Kirsten Gallo, U. S. Forest Service
Snow Creek, Deschutes County, Oregon: home of Geissleria cascadensis

Original Description

  • Author
    Sovereign 1958
  • Length Range
    11-21 µm
  • Width
    6-9 µm
  • Striae in 10µm

Original Images

Navicula Cascadensis Origimag001
Navicula Cascadensis Origdesc001


May 29, 2019 - Transfer to Geissleria

From 4/17/2016 until 5/29/2019, the taxon on this page appeared as Navicula cascadensis Sovereign 1958. The genus is now shown as Geissleria, to reflect the transfer:

"Navicula cascadensis Sovereign (1958: 118, pl. III: figs 32, 33) was initially an invalid name as no type was designated as required after 1 January 1958 (ICN Art. 40.1, Turland et al. 2018). As the protologue included collections from Diamond Lake and the nearby Crescent Lake (both located in the Cascade Mountain Range in southern Oregon), ICN Art. 40.2, which allows for a “entire gathering” to be an acceptable indication of type, does not apply. However, Sovereign (1960: 345) subsequently validated the name by designating a holotype slide in the CAS Diatom Collection."

Stancheva and Spaulding (2019)

Cite This Page

Bahls, L. (2016). Geissleria cascadensis. In Diatoms of North America. Retrieved July 15, 2024, from https://diatoms.org/species/navicula_cascadensis


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