Xanthidium

For the plant genus, see Ragweed.

Xanthidium is a genus of green algae, specifically of the Desmidiaceae.^[2]

Xanthidium
Scientific classification
Kingdom:	Plantae
Class:	Zygnematophyceae
Order:	Desmidiales
Family:	Desmidiaceae
Genus:	Xanthidium Ehrenb. ex Ralfs, 1848
Type species
Xanthidium aculeatum Ehrenb. ex Ralfs [1]
Species[1]
X. aculeatum X. antilopaeum X. armatum X. brebissonii X. cristatum X. hastiferum X. impar X. regulare X. subhastiferum X. superbum X. trilobum

The name Xanthidium is a diminutive of Xanthium, and presumably refers to its spines, reminiscent of the prickly fruits of Xanthium.^[3]

Description

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.^[4][5] 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.^[6]

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.^[7]

Habitat

Like other desmids, most species of Xanthidium prefer acidic waters.^[8]