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 µm;
- orientation: radiate, parallel, or convergent;
- chambering: whether an alveolus or not;
- seriation: whether uni-, bi-, or multiseriate.

Gomphoneis Geitleri Ex 1
Image Credit: Marina Potapova
External view of Gomphosinica geitleri showing the multiseriate striae.
46104  Sem2 1
Image Credit: Marina Potapova
External view of Navicula tripunctata showing the lineolate areolae composing the uniseriate striae.
A33 Sei 037
Image Credit: Megan Otu
External view of Cavinula pseudoscutiformis showing the uniseriate, radiate striae.