Phylogeny and biogeography of the staghorn fern genus Platycerium (Polypodiaceae, Polypodiidae).

The genus Platycerium is one of the few pantropical epiphytic fern genera with six species in Afro-Madagascar, 8-11 Australasian species, and a single species in tropical South America. Nucleotide sequences of four chloroplast DNA markers are employed to reconstruct the phylogeny of these ferns and to explore their historical biogeography. The data set was designed to resolve conflicting hypotheses on the relationships within the genus that were based on previous phylogenetic studies exploring morphological evidence. Our results suggest a basal split of Platycerium into two well-supported clades. One clade comprises species occurring in Africa, Madagascar, and South America, whereas the second clade contains exclusively Australasian species. The latter clade is further divided into a clade corresponding to P. bifurcatum and its putative segregates and a clade of seven species occurring from Indochina throughout the Malesian region to New Guinea and Australia. The Afro-Madagascan clade includes a clade of two species found in tropical Africa and a clade of four species that includes three species endemic to Madagascar. The single neotropical species of this genus, P. andinum, is nested within the Afro-Madagascan clade but is not closely related to any extant species.