Visit us at

Diatoms of the United States is now known as Diatoms of North America.
This site has been redesigned and updated, and will be closing soon.

Plagiotropis arizonica

Czarn. and Blinn 1978      Category: Symmetrical biraphid

Placoneis gastrum


Plagiotropis lepidoptera var. proboscidea

LM scalebar = 10 µm = 20 pixels.


Contributor: Loren Bahls - February 2012
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.

Original Description

Author: Czarn. and Blinn 1978
Length Range: 112-156 µm
Width Range: 17-24 µm
Striae in 10 µm: 16-19

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.

Original Images

Cite This Page:
Bahls, L. (2012). Plagiotropis arizonica. In Diatoms of the United States. Retrieved May 23, 2018, from

Species: Plagiotropis arizonica

Contributor: Loren Bahls

Reviewer: Rex Lowe


Czarnecki, D.B. and Blinn, D.W. (1978). Observations on southwestern diatoms. I. Plagiotropis arizonica n. sp. (Bacillariophyta, Entomoneidaceae), a large mesohalobous diatom. Transactions of the American Microscopical Society 97 (3): 393-396.

Czarnecki, D.B., Blinn, D.W. and Grim, J.N. (1980). Aspects of valve morphology in Plagiotropis arizonica, a diatom with an imperforate siliceous covering. Transactions of the American Microscopical Society 99 (4): 445-447.

Paddock, T.B.B. (1988). Plagiotropis Pfitzer and Tropidoneis Cleve, a summary account. Bibliotheca Diatomologica (H. Lange-Bertalot, ed.). Vol. 16. J. Cramer, Berlin, 152 pp. .

Links & ID's

Index Nominum Algarum (INA)

Original INA

California Academy of Sciences (CAS)

Plagiotropis arizonica CAS

North American Diatom Ecological Database (NADED)

NADED ID: 53003

Autecology Discussion

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.