Genetic relationships between Australian fireweed and south African and Madagascan populations of Senecio madagascariensis Poir. and closely related Senecio species

An isozyme and morphological study of Senecio madagascariensis Poir. and cl osely related species in Australia, South Africa and Madagascar was used to investigate the most likely region of origin for Australian plants known a s fireweed. Collections of seed and voucher specimens were made in New Sout h Wales, KwaZulu-Natal, East and West Cape Provinces and southern Madagasca r and specimens classified according to recognised taxa or descriptive vari ants. Plants were characterised by using isozyme analyses and morphological observations of both voucher specimens and achenes. Australian fireweed po pulations were found to be most closely related to populations of S. madaga scariensis from KwaZulu-Natal in South Africa, and to be more distantly rel ated to populations from East and West Cape Provinces in South Africa and f rom Madagascar. The implications of these findings are discussed in relatio n to efforts to locate host-specific biological control agents for fireweed .