Phytogeographic relationships between neotropical and African-Madagascan pteridophytes

Abstract

The purpose of this study is to determine the floristic affinities of pteridophytes between the neotropics and Africa-Madagascar and examine how these affinities might have arisen. We present an annotated list that contains two kinds of affinities: 1) species in common between both regions (excluding pantropical species) and 2) species pairs (or clusters of species paris) where one of the species (or infrageneric group) occurs in the Neotropics and the other in Africa and/or Madagascar. There are 114 examples on the list, of which 27 are same-species and 87 are species pairs or closely related taxa at some infrageneric level. About 13% of the African pteridoflora and 14% of the Madagascan pteridoflora show affinities with the Neotropics. To determine how these similarities might have originated, we assess three hypotheses: 1) the boreotropics hypothesis, 2) continental drift, and 3) long-distance dispersal. The boreotropics hypothesis is difficult to assess without further phylogenetic information on the groups to which the species belong. Continental drift seems to best explain one example in the geologically old family Schizaeaceae (species inAnemia subgen.Coptophyllum sect.Tomentosae). Nearly all the other examples seem best explained by long-distance dispersal because they belong to families that first appeared during the Paleocene, more than 30 million yearsafter drift had effectively separated South America and Africa. Most of the dispersal events appear to have taken place from the neotropics to Africa-Madagascar, but recent African extinctions may have obscured directionality. Species with green spores or gemmiferous gametophytes were slightly overrepresented on the list compared to pteridophytes as a whole.