Segregation of the polyphyletic genus Polyalthia (Annonaceae)

Abstract

The circumscription of the species-rich genus Polyalthia (Annonaceae, with ca. 150 species) has long been recognised to be highly problematic. The genus has functioned as a ‘dustbin group’ for species of unclear affinities due to the absence of clear synapomorphies, resulting in a morphologically heterogeneous species assemblage. Recent molecular phylogenetic analyses have indicated that Polyalthia is highly polyphyletic, with species scattered in multiple clades. The ‘Polyalthia hypoleuca complex,’ including Asian Polyalthia species with columellar-sulcate pollen, was recently segregated to form a new genus, Maasia. A considerably broader taxonomic sampling of Polyalthia species and associated taxa is included in the present phylogenetic analyses, with the objectives of increasing tree resolution and statistical support, hence enabling the recognition of strictly monophyletic genera with clearly defined diagnostic morphological characters. Bayesian and maximum parsimony analyses of chloroplast matK, rbcL and trnL-F DNA sequences consistently gave congruent topologies, with Polyalthia species distributed in five well-supported clades. Based on molecular and morphological data, existing Polyalthia species can be classified into the following five genera: (1) Fenerivia: 10 Madagascan Polyalthia species with columellarsulcate pollen form a well-supported clade distinct from Maasia. The generic name Fenerivia is reinstated for this clade since the type species Fenerivia heteropetala (=Polyalthia heteropetala) is included. (2) Marsypopetalum: five Asian Polyalthia species with thick inwardly-curved inner petals form a well-supported clade with Marsypopetalum pallidum (sister to Trivalvaria) and will be accordingly transferred to Marsypopetalum. (3) Enicosanthum: several Polyalthia species which belong to Polyalthia section Monoon (with a solitary, basal ovule in each ovary) form a wellsupported clade (sister to Neo-uvaria) together with some Enicosanthum species, Woodiellantha sympetala and Cleistopetalum borneense (a synonym of Polyalthia sinclairiana). (4) A new, currently unnamed genus: based on a well-supported clade consisting of several Polyalthia species, sister to Miliusa. (5) Polyalthia sensu stricto: the ‘true’ Polyalthia clade, including the type species, Polyalthia subcordata, and other species in Polyalthia section Polyalthia (with more than two ovules per ovary) as well as species in the small Australian endemic genus Haplostichanthus. The name Haplostichanthus will accordingly be recognized as a synonym of Polyalthia sensu stricto.