Guide to Fragilariforma
- Central sternum very narrow, or absent
- Cells joined by spines to form colonies
- Striae uniseriate
- Single rimoportula present at pole, in line with a stria
The valve margins of Fragilariforma are variable and may be linear, lanceolate, or elliptical with rostrate to capitate apices. In girdle view, frustules are rectangular in shape. Fragilariforma valves are characterized by a very narrow, or absent, central sternum. Striae are composed of distinct, uniseriate areolae. Frustules form linear colonies, linked by small marginal spines into ribbon like (band-shaped) colonies. A single rimoportula is present at one pole and is aligned with a stria. Living cells contain multiple discoid plastids.
Some species of Fragilariforma grow in ephemeral habitats, subject to periodic drying. In such habitats, frustules often form internal valves. Several species are typical of boreal wetlands and others are endemic to subtropical regions.