Molecular phylogenetics of Polyalthia (Annonaceae): identifying clades and morphological synapomorphies in alarge polyphyletic genus

Abstract

The genus Polyalthiais one of the largest genera in the early-divergent angiosperm family Annonaceae, with ca. 155 currently accepted species. The genus has long been recognised as a morphologically heterogeneous assemblage lacking conspicuous synapomorphies, and is one of the most significant impediments to revisionary and floristic taxonomic research in the family. The polyphyletic status of the genus has been confirmed in several molecular phylogenetic studies, with several other genera (Enicosanthum, Fenerivia, Haplostichanthus, Marsypopetalum, Monoon, Trivalvariaand Woodiellantha)either closely related to or with species formally assigned to Polyalthia.

This thesis presents the most comprehensive molecular phylogenetic study of Polyalthiato date, including 44Polyalthiaspecies and 16 species from putatively related genera. The phylogeny was reconstructed using maximum parsimony (MP), maximum likelihood (ML) and Bayesian inference (BI)methods, based on three chloroplast DNA regions (matK, rbcLand trnL-F). The Polyalthia species are shown to segregate into four clades: (I) a clade sister to Miliusa; (II) a clade that includes four Polyalthia species and also Marsypopetalum pallidum, sister to Trivalvaria; (III) a clade that also includes all Enicosanthum and Woodiellantha species sampled, sister to Neo-uvaria; and (IV) a clade that also includes all Haplostichanthus species sampled, sister to Popowia. All four identified Polyalthia clades are located in the tribe Miliuseae.

In order to assess the relationships among different Polyalthia clades as well as the relationships among all the genera in Miliuseae, a pilot study on the phylogenetic utility of a wide range of markers was carried out. Based on the result, eight chloroplast markers (matK, rbcL, trnL-F, psbA-trnH, ndhF, ndhF-rpl32, rpl32-trnLand ycf1) were selected and further sequenced for the clade representatives. Although unsuccessful in resolving the Miliuseae, the recognition of three of the four Polyalthia clades as monophyletic genera was confirmed.

Diagnostic morphological and anatomical characters were evaluated for clades II–IV, with the emphasis on putative synapomorphies. The morphology of the species not sampled for molecular study was examined in detail and compared against diagnostic characters to determine correct taxonomic placement. Based on the results, five Polyalthia species are transferred to Marsypopetalum. The generic name Monoon is resurrected for the clade that includes Enicosanthum and Woodiellantha, with the transfer of 37 species from Polyalthia s.l., 18 species from Enicosanthum and one Woodiellantha species. The generic name Haplostichanthus is synonymised with Polyalthias.str., with the 11 Haplostichanthus species transferred to Polyalthias.str..

The eight Polyalthia species reported from Fiji were further sampled in a phylogenetic reconstruction based on three markers (matK, rbcLand trnL-F). Three groups were identified, allied with Goniothalamus, Polyalthia Clade I and Meiogyne respectively.

The flower of Fenerivia capuronii (Cavaco & Keraudren) R.M.K. Saunders was selected for anatomical studies to examine whether the flange represents a reduced calyx as suggested for F. heteropetala and thus to test a possible homoetic mutation in F. capuronii. The results show that there is no vascular supply in the flange of F. capuronii, and that the putative homeotic change within Feneriviais therefore likely to only occur in F. heteropetala.