The taxonomic and evolutionary significance of some juvenile characters in the Brassiceae

Abstract

The shape of the cotyledon lamina and a few other juvenile characters are studied for some 140 taxa of the cruciferous tribe Brassiceae. They cast a number of doubts on the present botanical status of certain taxa, such as Diplotaxis siifolia, Erucastrum cardaminoides and Brassica balearica. The whole tribe Raphaninae appears rather unnatural when viewed from cotyledon evidence, which suggests that beak development and/or fruit reduction have evolved on different occasions. A primitive cotyledon type seems to be that showed by the genus Sinapidendron. It is nowadays still present in Brassica balearica, Oudneya africana and the oriental genus Orychophragmus. Some phenetic lines now represented by Moricandia, Foleyola, Hemicrambe, Diplotaxis and Brassica repanda may indicate ancient evolutionary trends derived from the primitive Sinapidendron-like Miocenic stock. Brassica ancestors could have either resembled B. repanda or evolved along the phenetic line now represented by the Diplotaxis Erucastrum-Brassica complex. A diphyletic or polyphyletic origin for the genus Brassica becomes thinkable.