Xanthidium exists as symmetrical single cells. 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. Semicells often have a protuberance or additional spine in the center of the semicell. Cells have two or many axile
chloroplasts which fill the cell. A notable exception is the species
Xanthidium tumidum, formerly placed in the genus
Staurastrum as
Staurastrum tumidum. Morphologically it is triangular in cross section (unlike other species, which are flattened in cross section). Its placement in this genus is due to molecular data.
Identification Species identification of
Xanthidium depends on the shape of the cell, cell wall ornamentation, and location and number of the spines. However, some species such as
Xanthidium antilopaeum are notoriously polymorphic. == Habitat ==