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Fragilariforma acidobiontica

(Charles) D.M.Williams and Round 1988      Category: Araphid
BASIONYM: Fragilaria acidobiontica Charles 1986
SYNONYM(S): Neofragilaria acidobiontica (Charles) D.M.Williams and Round 

Fragilaria vaucheriae


Fragilariforma bicapitata

LM scalebar = 10 µm = 80 pixels.


Contributor: David R.L. Burge - December 2015
Length Range: 32-67 µm
Width Range: 3-4 µm
Striae in 10 µm: 12-14 in the center valve, 14-15 at the ends


Valves are linear with rostrate ends. Striae are uniseriate and parallel throughout the valve. A narrow, hyaline interruption of the striae is present submarginally on the same side of the valve as the rimoportula (best seen in SEM). In girdle view, valves are rectangular and 4.3-6.1 µm in depth. Frustules often form band-shaped colonies, joined by marginal linking spines.

Original Description

Basionym: Fragilaria acidobiontica
Author: Charles 1986
Length Range: 22-86 µm
Width Range: 3-4.5 µm
Striae in 10 µm: 10-14

Original Description

Frustules narrowly rectangular in girdle view, 2-7µm along the pervalvar axis forming flat, ribbon-like colonies. Valve linear to linear-lanceolate with small, slightly asymmetrical, rostrate to slightly capitate apices. Length 22-86µm, breadth of valve 3.0-4.5µm. Valves held together by linking-spines present along the margin of the valve face. Spines lobate at apices, becoming bilobate to more complex toward mid-valve region. Axial area and central area lacking; striae continuous across middle of valve face. Striae interrupted along one margin, forming a narrow discontinuous line along the length of the valve, often indiscernible with the light microscope. Striae 10-14 in 10µm on valve face and valve mantle, denser toward ends, parallel throughout. Striae composed of punch, about 50 puncta in 10 µm. Labiate process at apex, offset toward side of valve with interrupted striae. Acidobiontic, occurs primarily in dilute waters with pH less than 5.5. Found in surface sediments of lakes in the Adirondack Park, New York and New Hampshire, USA, and Ontario, Canada.

Original Images

Cite This Page:
Burge, D. (2015). Fragilariforma acidobiontica. In Diatoms of the United States. Retrieved May 20, 2018, from

Species: Fragilariforma acidobiontica

Contributor: David R.L. Burge

Reviewer: Rex Lowe


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.

Donald F. Charles. (1986). A new diatom species, Fragilaria acidobiontica, from acidic lakes in northeastern North America. In: Smol, J.P., Barttarbee, R.W., Davis, R.B. and Meriläinen, J. (eds.), Diatoms and Lake Acidity. Dr. W. Junk Publishers, Dordrecht. pp. 35-44. ISBN 90 6193 536 9.

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)

Original INA
Transfer INA

California Academy of Sciences (CAS)

Fragilariforma acidobiontica CAS

North American Diatom Ecological Database (NADED)

NADED ID: 192018

Autecology Discussion

Charles (1986) named F. acidobiontica given the characteristic nature of it’s occurrence in low pH lakes, Camburn and Charles (2000) further corroborate the previous findings with occurrences from lakes with 5.5 ph or lower. Fragilariforma acidobiontica is often found occurring with other acidophiles such as Oxyneis, Semiorbis, and Actinella punctata.

The known distribution of F. acidobiontica is currently limited to surficial sediments of low alkalinity lakes in the Adirondacks of New England, USA and Ontario, Canada (Camburn and Charles 2000).