Weeds and aliens in Africa: the American immigrant: an inaugural lecture given in the University College of Rhodesia on 10th October, 1967

Abstract

South Central Africa are of tropical South American or Central American origin. In the case of the Heliantheae tribe of the Compositae which has recently been revised for the Flora Zambesiaca area, 28% of the Heliantheae are American in origin, cosmopolitan or pantropical weeds comprise 10%, African weeds 10%, and none come from Europe. 50% are non-weedy species. Of the important weeds of Rhodesia of all flowering plant families, American weeds consitute 32%, Mediterranean and European weeds 9%, Eurasian or Asiatic weeds 4%, pantropical or cosmopolitan weeds 15%, and African weeds 39%. Although the Anglo-Boer war at the beginning of this century is often said to be responsible for the introduction of many weeds, including the Khaki weeds Alternanthera pungens and Tagetes minuta, to southern Africa in fodder, etc., it is shown that many American weeds have been recorded from tropical Africa from the early nineteenth centrury onwards.