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Fragilaria pennsylvanica

E.Morales 2003      Category: Araphid

Fragilaria mesolepta


Fragilaria recapitellata

LM scalebar = 10 µm = 80 pixels.


Contributor: Gina LaLiberte - November 2015
Length Range: 13-26 µm
Width Range: 1.8-2.2 µm
Striae in 10 µm: 19.2-21.6


Valves are small, narrow and linear to linear-lanceolate, tapering to narrow rostrate apices. The axial area is broadly lanceolate. Striae are short, marginal, alternating and slightly radiate. The central area is variable, with striae slightly shortened on one side and absent on one side, or absent on both sides. The absence of striae makes the central area appear hyaline when viewed with the light microscope, but when enlarged and enhanced in photographs the central area may appear to have ghost striae.

Original Description

Author: E.Morales 2003
Length Range: 12-24.5 µm
Width Range: 1-2.5 µm
Striae in 10 µm: 18-22

Original Description

Length: 12–24.5 μm, width: 1–2.5 μm, striae: 18–22 per 10 μm. Central area clear on one or both sides (Figs. 20, 22). Central sternum wide and lanceolate (Figs. 20–26). Striae alternate and short, composed of round to slightly apically elongated areolae. Up to four areolae located on valve face and up to two on the valve mantle per stria. Volae were not observed. Spines absent. Apical pore fields of the ocellulimbus type with three to four rows of vertical poroids (Figs. 25–26). One rimoportula present (Figs. 24, 25). Girdle bands closed apparently bearing small isolated unoccluded perforations (Figs. 27–29). Plastids unknown.

Original Images

Cite This Page:
LaLiberte, G. (2015). Fragilaria pennsylvanica. In Diatoms of the United States. Retrieved May 20, 2018, from

Species: Fragilaria pennsylvanica

Contributor: Gina LaLiberte

Reviewer: Eduardo A. Morales


Morales, E.A. (2003). Fragilaria pennsylvanica, a new diatom (Bacillariophyceae) species from North America, with comments on the taxonomy of the genus Synedra Ehrenberg . Proceedings of the Academy of Natural Sciences of Philadelphia 153: 155-166.

Links & ID's

Index Nominum Algarum (INA)

Original INA

California Academy of Sciences (CAS)

Fragilaria pennsylvanica CAS

North American Diatom Ecological Database (NADED)

NADED ID: 1107

Autecology Discussion

Morales (2003) noted that Fragilaria pennsylvanica likely forms sessile stellate colonies. The Pennsylvania streams in which it has been found so far are non-calcareous and have relatively warm temperatures (21-27°C) during the growing season (Morales 2003).