Floristic exchange between mainland Africa and Madagascar: Case studies in Apocynaceae-Asclepiadoideae

 

Ulrich Meve & Sigrid Liede

 

Abstract:

Aim  The Apocynaceae-Asclepiadoideae (ca. 125 species) of Madagascar´s flora are highly endemic, and floristic conformity between Madagascar and Africa (and Asia) is low. Of the ca. 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Methods  Published and unpublished data on distribution, morphology, chromosome numbers and DNA sequence analysis of Asclepiadoideae taxa distributed in both Africa and Madagascar (Asia and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.

 

Main conclusions  An exchange of asclepiadaceous flora between mainland Africa and Madagascar and vice versa took place in at least ten cases. However, less than 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

Anemochory, Africa, Apocynaceae-Asclepiadoideae, Comoros Islands, long distance dispersal, Madagascar, polyploidy