Toward a New Generic Delimitation in Polygalaceae III: Chamaebuxus, Chodatia, Heterosamara, and Paivanthus

The Chamaebuxus alliance (Polygalaceae) comprises the Old World genera Heterosamara Kuntze, Chamaebuxus Tourn. (formerly known as Polygaloides Haller), and Polygala L. subg. Chodatia Paiva and represents the last unresolved lineage of Polygala s.l. that has not yet been comprehensively analyzed in a phylogenetic study. Based on phylogenetic and morphological evidence, we accommodate these taxa into four distinct genera: Chamaebuxus, Chodatia (Paiva) J. F. B. Pastore, comb. & stat. nov. (elevated to genus rank), Heterosamara, and Paivanthus J. F. B. Pastore, gen. nov. Phylogenetic trees were inferred using target enrichment data with Angiosperms353 probes, complemented by data from the maternally inherited plastid loci and the biparentally inherited nrITS region. A strongly supported topological incongruence was observed between the plastid and nuclear datasets for the African genus Paivanthus, which was recovered as sister to Chodatia in plastid analyses, but as sister to the Asiatic genus Heterosamara in nuclear analyses. This incongruence suggests a likely hybrid origin for the African lineage formerly included in Heterosamara. Here, Polygala subg. Chodatia is raised to generic rank, encompassing the species formerly alternatively assigned to Polygala sect. Arillus S. K. Chen. Within Chamaebuxus, we recognize two sections: the Old World section Chamaebuxus and the North American monotypic section Triclisperma (Raf.) J. F. B. Pastore. Two genera are now recognized as having heteropolar pollen: Heterosamara s. str. and Paivanthus, which includes African species previously assigned to Heterosamara. The genus Heterosamara is further subdivided into five sections: section Ecristata J. F. B. Pastore (newly described), section Heterosamara, section Saxicola S. K. Chen, section Spathulata J. F. B. Pastore (newly described), and section Villososperma C. Y. Wu & S. K. Chen. A taxonomic key is provided for the genera Chamaebuxus, Chodatia, Heterosamara, Paivanthus, and Polygala, along with their infrageneric taxa. Photographic plates, a distribution map, 15 new lectotypes, six second-step lectotypes, two new heterotypic synonyms, 41 new combinations, and nomenclatural notes are also presented.