Fragilariforma polygonata

(A.Cleve) Kingston, Sherwood and Bengtsson 2001      Category: Araphid
BASIONYM: Fragilaria polygonata A.Cleve 1953

Fragilariforma nitzschioides


Fragilariforma virescens

LM scalebar = 10 µm = 80 pixels.


Contributor: David R.L. Burge | Mark Edlund - March 2017
Length Range: 22-30 µm
Width Range: 9.8-10.5 µm
Striae in 10 µm: 19-20


Large valves are lanceolate with tri-undulate margins, smaller valves are rhombic-lanceolate. Central undulation is the widest part of the valve and the apical undulations are more pronounced in larger specimens. Apices are broadly tapered, with rounded apices. A narrow sternum is present. Striae are parallel at the valve center, becoming radiate and slightly curved toward the apices.

Kingston et al. (2001) neotypified Fragilariforma polygonata using Newfoundland material after extensive search of Cleve-Euler’s (1953) syntypes showed no valves of “Fragilaria polygonata” present. The concept presented here follows Kingston et al. (2001).

Original Description

Basionym: Fragilaria polygonata
Author: A.Cleve 1953
Length Range: 32-34 µm
Width Range: 8.5-10 µm
Striae in 10 µm: 20

Original Description

F. polygonata n. sp. Schalen linear-lanzettlich mit einer mittleren, beiderseitig rechtwinklig u. keilig zugespitzten Ausstülpung, an beiden Seiten der Ausstülpung meistens leicht eingeschnürt. Enden entweder keilig verdünnt, stumpf gestutzt, oder apikulat, in eine schmale Spitze auslaufend. Pseudoraphe nicht hervortretend, Str. parallel u. fein, etwa 20 auf 10 µ. L. 32-34 µ. Br. 8,5-10 µ (Mitte), in den Einschnürungen 4,5-5,5 µ.

Original Images

Cite This Page:
Burge, D., and Edlund, M. (2017). Fragilariforma polygonata. In Diatoms of the United States. Retrieved April 21, 2018, from

Species: Fragilariforma polygonata

Contributor: David R.L. Burge | Mark Edlund

Reviewer: Eduardo A. Morales


Cleve-Euler, A. (1953). Die Diatomeen von Schweden und Finnland. Teil III. Monoraphideae, Biraphideae 1. Authorized Reprint 1968, Bibliotheca Phycologica, Band 5, J. Cramer, Lehre.

Kingston, J.C., Sherwood, A.R., & Bengstsson, R. (2001). Morphology and taxonomy of several Fragilariforma taxa from Fennoscandia and North America. In: Economou-Amilli, A. (ed.): Proceedings of the 16th International Diatom Symposium, Athens, Greece: 73–88. – Amvrosios Press, Athens, Greece.

Siver, P.A. and Hamilton, P.B. (2011). Diatoms of North America: The Freshwater Flora of Waterbodies on the Atlantic Coastal Plain. Iconographia Diatomologica 22.

Links & ID's

Index Nominum Algarum (INA)

California Academy of Sciences (CAS)

Fragilariforma polygonata CAS

North American Diatom Ecological Database (NADED)

NADED ID: 192011

Autecology Discussion

Fragilaria polygonata is reported from dystrophic New England lakes (Kingston et al. 2001) south to North Carolina (Siver and Hamilton 2011). Specimens illustrated here are from a boreal river in northern Minnesota in waters high in dissolved organic carbon.


The distribution of F. polygonata in rivers of the United States. Accessed on 17 July, 2017.

Credit/Source: USGS/Biodata