The genus Amsinckia Lehm. (Boraginaceae) in southern Africa

The genus Amsinckia (Boraginaceae / Boraginoideae / Eritrichieae) comprises ± 15 species, all native to the western United States, with California the centre of diversity. In southern Africa only A. retrorsa Suksd., most probably introduced by means of wheat seed, has established itself in the Northern and Western Cape, sporadically also occurring in other parts of the country. It is an annual herb characterised by small, yellow or orange-yellow flowers borne in terminal, cymose inflorescences with cymules helicoid, elongating and uncoiling in the fruiting stage, typical of Boraginaceae. A. retrorsa has retrorse hairs on the stems and the nutlets are ovoid-trigonous, rugose, tuberculate and verrucose with Verrucae minutely muricate. These characters distinguish A. retrorsa from other members of the family in southern Africa. The 6-heterocolpate pollen grains of A. retrorsa show similarity to those of Heliotropium L. (Boraginaceae, subfamily Heliotropioideae), but the presence of a gynobasic style, not terminal as in Heliotropium, still places A. retrorsa in Boraginaceae s.l., subfamily Boraginoideae. Diagnostic characters, a full description, various illustrations and a distribution map of A. retrorsa are given