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A stria is a row of areolae or alveoli. Latin for groove or stripe. Plural is striae.
In centric diatoms, striae are usually oriented along radii of a valve. In pennate diatoms, striae are usually oriented on the valve more or less transapically.
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.