• Category
  • Length Range
    147-180 µm
  • Width Range
    24-31 µm
  • Striae in 10 µm
    13-15 (center); 16-17 (ends)



Valves are linear-lanceolate with apiculate apices. The axial area is very narrow and the central area is small and circular. The raphe is filiform and positioned on the narrow apex of a bilobed keel. Proximal raphe ends are simple and straight. Striae are distinctly punctate and parallel, but slightly convergent and more widely spaced near the valve center. Areolae are distinct in LM and number 15-18 in 10 µm.


There are 18 records of Plagiotropis arizonica in the Montana Diatom Collection, all of them from streams and one lake on the Northwestern Great Plains in eastern Montana and western South Dakota. The mean pH of these waters is 8.7 and the mean specific conductance is 4768 μS/cm. Sodium is the most abundant cation at a mean concentration of 962 mg/L and sulfate is the most abundant anion (mean concentration = 1232 mg/L). Common diatom associates of P. arizonica in the region are Amphora tumida, Amphora delicatissima, Navicula curtisterna, Surirella striatula, Microcostatus naumannii, Navicula viliplanii, Nitzschia lacunarum, and Navicula cryptocephaloides. Czarnecki and Blinn (1978) report this species from the epiphyton, epipelon, and episammon communities of Cholla Lake and Chevelon Creek in northern Arizona.

Original Description

Frustule distinctly bilobate in girdle view; pseudosepta [later described as helictoglossae (Czarnecki et al. 1980)] evident at the termini of the valve. Valves linear-lanceolate with apiculate apices. Raphe straight, central, enclosed in the narrow apex of a bilobed keel. Central area small, elliptical or orbicular. Striae distinctly punctate, parallel, but slightly convergent and coarser near the central area, 16-19 in 10 µm; puncta 16-18 in 10 µm. Length 112-156 µm. Width (valve) 17-24 µm; (frustule at the center in girdle view) 19-30 µm.

  • Author
    Czarn. and Blinn 1978
  • Length Range
    112-156 µm
  • Width
    17-24 µm
  • Striae in 10µm

Original Images

Plagarizon Origimag1
Plagarizon Origimag2 1
Plagarizon Origimag3 2
Plagarizon Origdesc

Cite This Page

Bahls, L. (2012). Plagiotropis arizonica. In Diatoms of North America. Retrieved August 18, 2018, from https://diatoms.org/species/plagiotropis_arizonica


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