Xanthidium is a genus of green algae, specifically of the Desmidiaceae.

Cells are deeply constricted, forming two halves called semicells; they are rectangular, rounded, or polygonal in front view, flattened.

The angles are usually drawn out into spines, which are typically paired and sometimes branched.

However, some species such as Xanthidium antilopaeum are notoriously polymorphic.

[6] Like other desmids, most species of Xanthidium prefer acidic waters.