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Species well-travelled: understanding balloon vine biogeography

Cardiospermum grandiflorum

The native geographic distribution of the cosmopolitan genus Cardiospermum, commonly known as balloon vines, is unknown. In many parts of the world balloon vines are variously considered to be native, invasive or simply of unknown origin. A recent review paper published in the journal NeoBiota by MSc student Enelge Gildenhuys and C·I·B core team member Dr Jaco Le Roux indicates that part of the problem lies with the extensive movement of balloon vines around the world by humans for medicinal and ornamental purposes. Cardiospermum species are used by many people in rural areas for medicinal purposes.

This paper demonstrates that although at least one species, C. grandiflorum, is considered a serious invader in South Africa, two sister species, C. corindum and C. halicacabum, are of unknown native/alien status. This uncertainty prevents the release of identified biological control agents in South Africa, because of concerns that they may also affect the possibly native sister species. Enelge’s phylogenetic analysis indicated that C. halicacabum is probably also alien to southern Africa, while C. corindum may have arrived in Africa through natural long distance dispersal and should therefore be considered native. These findings imply that biological control agents capable of feeding on C. corindum should not be released in South Africa.

Prevention is better than cure for invasive species management, and eradication become less and less feasible as invasions progress. A crucial step in prevention is determining which areas are suitable for establishment of alien species. Enelge and her colleagues used a computer-based model to identify areas from which balloon vines are currently absent, but which have suitable climate conditions, and which may be colonised in future. They found several such areas adjacent to currently-occupied areas, suggesting that balloon vines have the potential to spread further in already occupied parts of Australia, Africa and Asia. The researchers also assessed the accuracy of this commonly-employed modelling method and concluded that species distribution modelling often exaggerate predicted suitable ranges, and that factors other than climate frequently influence establishment potential.

This review paper opens the door to a better understanding of the global biogeography of the genus Cardiospermum, with direct implications for invasive species management and future research.




Read the paper:

Gildenhuys, E., Ellis, A.G., Carroll, S. & Le Roux, J.J. (2013) The ecology, biogeography, history and future of two globally important weeds: Cardiospermum halicacabum Linn. and C. grandiflorum Sw. NeoBiota 19: 45–65. doi: 10.3897/neobiota.19.5279.

For more information contact, Dr Jaco Le Roux at jleroux@sun.ac.za

Typical invasion of Cardiospermum grandiflorum in South Africa

Typical invasion of Cardiospermum grandiflorum in South Africa. The balloon vine completetly covers native vegetation, preventing sunlight to penetrate through to the undelying vegetation, hence preventing photosynthesis.