Fragilariforma constricta

(Ehrenb.) D.M.Williams and Round 1988      Category: Araphid
BASIONYM: Fragilaria constricta Ehrenb. 1843
SYNONYM(S): Neofragilaria constricta D.M.Williams and Round 

Fragilariforma bicapitata


Fragilariforma horstii

LM scalebar = 10 µm = 80 pixels.


Contributor: David R.L. Burge | Mark Edlund | Lynn Brant - October 2016
Length Range: 22-40 µm
Width Range: 3.7-5.9 µm
Striae in 10 µm: 16-24


Valves linear-lanceolate with a constricted center resulting in bi-undulate margins. The rostrate to capitate apices are attenuate, ending bluntly rounded and bearing apical pore fields. Striae are parallel throughout, sometimes slightly curved at the widest portion of valve. Narrow sternum present. Spines may be visible in LM, occurring between striae along the valve face-mantle junction. A single rimoportula is located near one of the apices, and is difficult to distinguish in LM.

The concept of Fragilariforma constricta presented here conforms to most authors’ species concept (Patrick and Reimer 1966, Krammer and Lange-Bertalot 1991, Camburn and Charles 2000, Kingston et al. 2001, Siver and Hamilton 2011); however, the syntypes illustrated by Ehrenberg (Falkland Islands and Montezuma River) do not clearly match the current taxonomic concept of this taxon. Analysis of Ehrenberg’s material may change the taxonomic concept of F. constricta.

Original Description

Basionym: Fragilaria constricta
Author: Ehrenb. 1843
Length Range: µm
Striae in 10 µm:

Original Description

Original Images

Cite This Page:
Burge, D., Edlund, M., and Brant, L. (2016). Fragilariforma constricta. In Diatoms of the United States. Retrieved April 19, 2018, from

Species: Fragilariforma constricta

Contributor: David R.L. Burge | Mark Edlund | Lynn Brant

Reviewer: Eduardo A. Morales


Camburn, K.E. and Charles, D.F. (2000). Diatoms of Low-Alkalinity Lakes in the Northeastern United States. Academy of Natural Sciences of Philadelphia, Special Publication 18, 152 pp.

Ehrenberg, C.G. (1843). Verbreitung und Einfluß des mikroskopischen Lebens in Süd- und Nord-Amerika. Abhandlungen der Königlichen Akademie der Wissenschaften zu Berlin, 1841: 291-445, 4 Tafel.

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.

Krammer, K. and Lange-Bertalot, H. (1991). Bacillariophyceae. 3. Teil: Centrales, Fragilariaceae, Eunotiaceae. In Ettl, H., Gerloff, J., Heynig, H. & Mollenhauer, D. (Eds.). Süsswasserflora von Mitteleuropa. 2(3): 1-576. Gustav Fisher Verlag, Stuttgart, Germany.

Patrick, R.M. and Reimer, C.W. (1966). The Diatoms of the United States exclusive of Alaska and Hawaii, V. 1. Monographs of the Academy of Natural Sciences of Philadelphia 13.

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.

Williams, D.M. and Round, F.E. (1987). Revision of the genus Synedra Ehrenb. Diatom Research 1(2): 313-339.

Williams, D.M. and Round, F.E. (1988). Fragilariforma, nom. nov., a new generic name for Neofragilaria Williams & Round. Diatom Research 3: 265-267.

Links & ID's

Index Nominum Algarum (INA)

Transfer INA
Original INA

California Academy of Sciences (CAS)

Fragilariforma constricta CAS

North American Diatom Ecological Database (NADED)

NADED ID: 192002

Autecology Discussion

Fragilariforma constricta is widely distributed in the eastern United States in low pH, dystrophic rivers (Patrick & Reimer 1966) and lakes (Camburn and Charles 2000). Siver and Hamilton et al. (2011) noted Fragilariforma constricta most abundant in New England states and very rare or absent from Mid-Atlantic States. Specimens illustrated here are from northern Minnesota.