The guest on this episode of the podcast is William Beinart, Rhodes Professor of race relations and director the African Studies Centre in Oxford. In the first part of the podcast, Professor Beinart critiques Alfred Crosby’s idea of ecological imperialism. He argues that from the vantage point of Africa, part of the ‘old world’, Crosby’s discussion of asymmetrical plant exchange is problematic. Many species from the America’s were highly successful in Africa. This applies both to cultivated crops and some semi-invasive or invasive plants. Beinart suggests that demographically, economically, and socially, the benefits have outweighed the costs of such invasive plants as prickly pear from Mexico and black wattle from Australia. The ecological costs have been greater but they are difficult to value. The podcast concludes with some brief comments on the relevance of a more flexible and less purist approach to concepts of biodiversity, and how this might be adapted to cater for transferred plants.