Comparisons of invasive plants in southern Africa originating from southern temperate, northern temperate and tropical regions

A subset of invasive alien plant species in southern Africa was analysed in terms of their history of introduction, rate of spread, countries/region of origin, taxonomy, growth forms, cultivated uses, weed status and current distribution in southern Africa, and comparisons made of those originating from south of the tropic of Capricorn, north of the tropic of Cancer and from the tropics. The sub set of 233 species, belonging to 58 families, includes all important declared species and some potentially important species. Almost as many species originate from temperate regions (112) as from the tropics (12 1). Most southern temperate species came from Australia (28/36), most tropical species from tropical America (92/121) and most northern temperate species from Europe (including the Mediterranean) and Asia (58/76). Transformers account for 33% of all species. More transformers are of tropical origin (36) than of northern temperate (24) and southern temperate origin (18). However, 50% of southern temperate species are transformers, compared to 32% of northern temperate and 29% of tropical species. Southern temperate transformer species are mainly woody trees and shrubs that were established on a grand scale as silvicultural crops, barriers (hedges, windbreaks and screens) and cover/binders. Most aquatics, herbs, climbers and succulent shrubs are from the tropics. Ornamentals are the single largest category of plants from all three regions, the tropics having contributed twice as many species as temperate regions.