Floristic exchange between mainland Africa and Madagascar: case studies in Apocynaceae– Asclepiadoideae

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Abstract:

Aim

The Apocynaceae–Asclepiadoideae (c. 125 species) of Madagascar's flora are highly endemic, and floristic conformity between Madagascar and Africa (and Asia) is low. Of the c. 1250 Old World Asclepiadoideae species, only ten species are shared between mainland Africa and Madagascar. Our comprehensive data elaborated during the last 15 years of systematic research in Asclepiadoideae were used to (1) examine Leroy's hypothesis that Madagascar's flora resulted from an autochthonous Gondwanean stock and natural introduction of taxa in time, (2) check the probability of our phylogentic considerations against the direction of the floristic exchange traced, and (3) present evidence for successful long-distance dispersal events. Location

Africa, Madagascar, Asia. Methods

Published and unpublished data on distribution, morphology, chromosome numbers and DNA sequence analysis of Asclepiadoideae taxa distributed in both Africa and Madagascar (Asia and Madagascar) were reviewed and evaluated. Results

Ten species belonging to the genera Ceropegia, Cynanchum (incl. Sarcostemma), Gomphorcarpus, Gymnema, Microloma, Pentatropis, Pleurostelma, Telosma and Tylophora are shared between mainland Africa and Madagascar, three species extend to Asia. In most of the cases presented, evidence points to long-distance dispersal from Africa to Madagascar; only in the Cynanchum complex dispersal events from Madagascar to Africa are corroborated. Mainconclusions

An exchange of asclepiadaceous flora between mainland Africa and Madagascar and vice versa took place in at least ten cases. However, <1% of the Malagasy species is involved, meaning that the speciose autochthonous Malagasy Asclepiadoideae flora is only inconspicuously influenced by these presumably rather recent introductions. The African–Malagasy distributions can only be explained by long-distance dispersal events effected by anemochorous seeds.

Keywords: Africa; Anemochory; Apocynaceae–Asclepiadoideae; Comoros Islands; Madagascar; long-distance dispersal; polyploidy

Document Type: Research Article

DOI: http://dx.doi.org/10.1046/j.1365-2699.2002.00729.x

Affiliations: Department of Plant Systematics, University of Bayreuth, 95440 Bayreuth, Germany

Publication date: July 1, 2002

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