Distribution, ecology and management of Cryptostegia grandiflora and Cryptostegia madagascarensis (rubber vine) in southern Africa

Distribution, ecology and management of Cryptostegia grandiflora and Cryptostegia madagascarensis (rubber vine) in southern Africa
Ludi Kern1,2,3, Peter C. Le Roux2, Michelle Greve2, John R. Wilson1, Peter Shisani1
1 Invasive Species Programme, SANBI; 2 University of Pretoria; 3Mogalakwena Research Centre

Cryptostegia grandiflora and C. madagascariensis (Rubber vine) originate from Madagascar where they are restricted to drier areas that receive 350-800 mm rainfall annually. Both species are serious invaders in climatically suitable countries across the world, including Australia where C. grandiflora is listed as a Weed of National Significance. In South Africa both Cryptostegia species are proposed for listing under NEM: BA as Category 1 (b) species. Some occurrence records exist for these species in urban  and  natural  areas  in  southern  Africa  and  one  of  these  species  (C.  grandiflora)  is  well established and invasive along the Mogalakwena River in the Limpopo Province. As a result, there is concern that C. grandiflora and C. madagascariensis could potentially pose a risk to sensitive unique riparian areas in South Africa. However, few occurrence data exist for these species in southern Africa making it difficult to determine the species' current distributions. Pilot surveys conducted along the Mogalakwena River in the Limpopo Province have shown that some areas have densities as high as  2000  plants/ha,  although  these  infestations  occur  no  further  than  40  m  away  from  the Mogalakwena River. Further fine scale surveys will be conducted along the Mogalakwena River to determine which variables influence the local distribution of Cryptostegia spp., while national- and global-scale occurrence records will be used to model potentially climatically suited risk areas where future search focus should be directed.