With more than 250 species, Xyris is taxonomically the most complex and
geographically the most widespread genus of the family. The largest concentration
of species and probably the chief centers of distribution of Xyris occur in
tropical America. The genus is prominently represented in marshy or wet areas
in Xorth America, Africa, Asia, and Australia, but is lacking in Europe.
Xyris has been divided taxonomically into three sections, viz., sect. Pomatoryn's Endlicher (Gen. PI. 124. 1841), characterized chiefly by a basally 3-locular capsule, with perhaps fewer than twenty species confined to Australia; sect. Euryris, characterized by a unilocular capsule and parietal placentation, of possibly more than one hundred pantropical and North American species; and sect. Ncmatopns Seubert (PI. Bras. 31: 211. 1855), in which the capsule is likewise unilocular, but the placentation basal, of probably more than one hundred species confined to tropical America.