Stria density and count in centric diatoms

A row of areolae on the valve. In centric diatoms, usually oriented along radii; in pennate diatoms, usually oriented more or less perpendicular to the apical axis. Plural form is striae.

Features of the striae are important in diatom taxonomy and phylogeny, such as:

- density: number of striae that occur in 10 ┬Ám;
- orientation: radiate, parallel, or convergent;
- chambering: whether an alveolus or not;
- seriation: whether uni-, bi-, or multiseriate.