Fragilaria

Fragilaria are thin and long diatoms which are often seen in long banded colonies. They're quite common in lakes worldwide. Like many diatoms, they display two distinct shapes depending on whether they're seen in valve view or girdle view. In girdle view, they appear to be shaped like rectangles or with a flared center and tips. In valve view, they take on the shape of a long oval, and striae are more clearly seen. It is very difficult to identify most species of Fragilaria without the valve view.

F. capuchina

F. capuchina is a widely variable species, to the point that there are many sub-species of it: F. vaucheriae and F. mesolepta are a few. In girdle view, the below specimen cannot be further identified. Those subspecies are described below.

Fragilaria capucina_edited

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F. crotoensis

Cells are 60-72 µm in length, 2-3 µm in width.
Rows of striae are 17-18 per 10 µm.
Central area takes up 1/3 to 2/3 of the valve face, and has 2-6 distinct depressions
Valves are thicker in the middle, very thin towards the ends, and the ends are capped with larger rounded ends.
Spines may be present.

For more information, visit diatoms.org here.

A3m1 Fragilaria crotonensis_edited

F. mesolepta

Cells are 13 - 44 µm in length, 2 - 3.5 µm in width.
Striae are 13 - 17 per 10 µm along the circumference.
Striae on each side of the valve may be aligned or slightly offset
Cells appear slightly "pinched" in the middle in valve view

For more information, visit diatoms.org here.

A3m3 Fragilaria mesolepta_edited

A3m3 Fragilaria mesolepta3_edited

A3m1 img Fragilaria mesolepta_edited

A3m3 Fragilaria mesolepta1_edited

A3m1 img Fragilaria mesolepta2_edited

A3m1 Fragilaria capucina var. mesolepta_edited

A3m1 img Fragilaria mesolepta1_edited

F. parasitica var. constricta

Cells are 16 - 19 µm in length, 4 - 5 µm in width.
Striae are 16 - 20 per 10 µm.
May be confused with Staurosira construens var. binodis, which has coarser striae and a narrower center.

For more information, visit craticula.uk here.

A5m1 Pseudostaurosira parasitica var. subconstricta_edited

F. vaucheriae

Cells are 16 - 30 µm in length, 4 - 5 µm in width.
Striae are 14 - 16 per 10 µm along the circumference.
Striae are absent at the center of the valve on one side.
Striae are broad and spaced widely

For more information, visit diatoms.org here.

A3m3 Fragilaria vaucheriae_edited

A5m1 Fragilaria vaucheriae (_)_edited

Mendota Diatoms

A local field guide to Wisconsin algae

Fragilaria

F. capuchina

F. capuchina is a widely variable species, to the point that there are many sub-species of it: F. vaucheriae and F. mesolepta are a few. In girdle view, the below specimen cannot be further identified. Those subspecies are described below.

F. crotoensis

Cells are 60-72 µm in length, 2-3 µm in width.

Rows of striae are 17-18 per 10 µm.

Central area takes up 1/3 to 2/3 of the valve face, and has 2-6 distinct depressions

Valves are thicker in the middle, very thin towards the ends, and the ends are capped with larger rounded ends.

Spines may be present.

For more information, visit diatoms.org here.

F. mesolepta

Cells are 13 - 44 µm in length, 2 - 3.5 µm in width.

Striae are 13 - 17 per 10 µm along the circumference.

Striae on each side of the valve may be aligned or slightly offset

Cells appear slightly "pinched" in the middle in valve view

For more information, visit diatoms.org here.

F. parasitica var. constricta

Cells are 16 - 19 µm in length, 4 - 5 µm in width.

Striae are 16 - 20 per 10 µm.

May be confused with Staurosira construens var. binodis, which has coarser striae and a narrower center.

For more information, visit craticula.uk here.

F. vaucheriae

Cells are 16 - 30 µm in length, 4 - 5 µm in width.

Striae are 14 - 16 per 10 µm along the circumference.

Striae are absent at the center of the valve on one side.

Striae are broad and spaced widely

For more information, visit diatoms.org here.