Molecular phylogenetics and historical biogeography of the Meiogyne-Fitzalania clade (Annonaceae): Generic paraphyly and late Miocene-Pliocene diversification in Australasia and the Pacific

Meiogyne (Annonaceae) comprises 15 species of trees and shrubs distributed in India, Indomalaya and Australasia-Pacific. Previous molecular phylogenetic analyses, based on limited taxon sampling, have indicated that the small genus Fitzalania (2 spp.) is nested within Meiogyne. The centre of diversity of the Meiogyne-Fitzalania group lies in Australia (6 spp.) and New Caledonia (4 spp.); this is unique in Annonaceae, some of whose Australian and New Caledonian lineages have been hypothesised to have originated in situ from Gondwanan ancestors. Phylogenetic reconstructions based on chloroplast DNA sequence data of 19 accessions, representing 14 of the 17 species in the Meiogyne-Fitzalania group (ca. 8.6 kb) as well as 67 representatives of all major clades of Annonaceae (ca. 5.1 kb), were performed to clarify the phylogenetic relationships of Meiogyne and Fitzalania. The results show that Fitzalania is deeply nested within an Australasian-Pacific clade of Meiogyne species. The inclusion of species assigned to Chieniodendron and Oncodostigma in Meiogyne, as proposed in the most recent revision of Meiogyne, is also corroborated. Fossil-calibrated molecular divergence estimates under an uncorrelated-rates relaxed molecular clock model were used to investigate the timing of the crown group diversification. The Meiogyne crown group was inferred to have originated in the late Oligocene or Miocene, and initially diversified in continental Southeast Asia, western Malesia and the Philippines. All Australasian-Pacific taxa formed a single derived clade, and most diversification within this clade occurred in the late Miocene and Pliocene. A complex combination of factors such as fragmentation of once wider distribution areas due to climate fluctuations and subsequent vicariance, range expansion by dispersal to Pacific islands and subsequent differentiation, and ecological adaptation to local climatic and edaphic habitat conditions is hypothesised to underlie the diversification of Meiogyne in Australasia and the Pacific.