Visit us at

Diatoms of the United States is now known as Diatoms of North America.
This site has been redesigned and updated, and will be closing soon.

Glossary terms starting with "u"


Usually refers to the morphological features of the frustule that are visible with a scanning electron microscope (SEM).


Having the shape of a wave, with crests and troughs. A valve may be undulate on the margins or on the face.


A stria having a single row of areolae. From Latin for one series.