Polypsecadium

Polypsecadium is a genus of large herbaceous species of plants in the family Brassicaceae, found growing in South America. Most of the species were formerly classified in the genus Sisymbrium.

==Taxonomy== Polypsecadium was first created in 1924 by the German botanist Otto Eugen Schulz to house P. harmsianum (the type species), which had earlier been described as a new species of Thelypodium in 1908. Schulz described a number of other related species in other genera. The genus remained monotypic until 1982, when the Argentine botanists M. C. Romanczuk and Osvaldo Boelcke added two new species. In their 2003 general work on Brassicaceae (Cruciferae) in the book series The families and genera of vascular plants, O. Appel and the Iraqi botanist Ihsan Ali Al-Shehbaz continued to recognise three species in the genus, but by this time, in the beginning of the 2000s, phylogenetic trees produced by molecular studies of the DNA were challenging the circumscription of the traditional genera -in other words, the traditional morphological characteristics were proving unreliable in delimiting monophyletic genera. One of these genera was Sisymbrium, which consisted of some 90 species from the end of the 1980s to the early 2000s, a large proportion of these from South America. The North American species of Sisymbrium had already been moved to new genera in 1976 by Rollins, except one (the wrong one, it later turned out). In 2006 Al-Shehbaz moved almost all of the South American representatives of the genus Sisymbrium to either new or existing genera, and in doing so increased the genus Polypsecadium to fourteen species. The last Sisymbrium species from the Americas (one still remains in North America) were moved by Al-Shehbaz in 2012.