Abstract

An isozyme and morphological study of Senecio madagascariensis Poir. and closely related species in Australia, South Africa and Madagascar was used to investigate the most likely region of origin for Australian plants known as fireweed. Collections of seed and voucher specimens were made in New South Wales, KwaZulu-Natal, East and West Cape Provinces and southern Madagascar and specimens classified according to recognised taxa or descriptive variants. Plants were characterised by using isozyme analyses and morphological observations of both voucher specimens and achenes. Australian fireweed populations were found to be most closely related to populations of S. madagascariensis from KwaZulu-Natal in South Africa, and to be more distantly related to populations from East and West Cape Provinces in South Africa and from Madagascar. The implications of these findings are discussed in relation to efforts to locate host-specific biological control agents for fireweed.