A stria having two rows of areolae.

Alternative Terms

doubly punctate
Much of the diatom literature uses "doubly punctate" to describe striae composed of two rows of areolae.
R Nodosum Areolae
Image Credit: Marina Potapova
Here, the biseriate striae of Rossithidium nodosum are shown in a SEM image. In some species, the biseriate striae are quite visible in LM. In other species, they may not be discernable without SEM.
G Loweii Biseriate
Image Credit: Pat Kociolek
Biseriate striae are a distinguishing character of the genus Gomphoneis. Here, the biseriate striae of G. loweii are prominent in an LM image.