A species-level phylogenetic framework and infrageneric classification for the genus Maesa (Primulaceae)

The systematization of Maesa, a genus of almost 200 species, has haunted taxonomists for more than a century due to its lack of distinct qualitative characters or discontinuities in quantitative characters for species delimitation. The clarification of phylogenetic relationships in such a problematic genus like Maesa is essential to aid infrageneric classification and species delimitation. Here, a species-level phylogenetic tree of Maesa is reconstructed. Leaf materials were sampled mainly from herbarium specimens which cover 60% of the species across the entire distribution range of the genus. Targeted sequence capture with the Angiosperms353 probe set was used to acquire sequences for downstream bioinformatic analyses. We obtained a species tree inferred from 310 gene trees that divides Maesa into an African clade and an Asian-Pacific clade. The African clade is further divided into two subclades, while the Asian-Pacific clade is divided into three subclades; all subclades are well supported. Hence, we propose five subgenera of Maesa, namely M. subg. Maesa, subg. Indicae, subg. Monotaxis, subg. Papuanae and subg. Ramentaceae. In addition, we scrutinize some species complexes within the genus; however, with the lack of phylogenetic signal at shallow levels, we are unable to conclusively resolve all species boundaries in these complexes. This study provides the phylogenomic framework to untangle taxonomic problems in the genus Maesa and lays the foundation for further detailed studies in biogeography, trait evolution and population genetics.

Automated summary

This study reconstructed a species-level phylogenetic tree of the genus Maesa, dividing it into African and Asian-Pacific clades, each further divided into two or three subclades. Five subgenera of Maesa were proposed based on this phylogenetic analysis. However, resolving species boundaries within some species complexes was challenging due to a lack of phylogenetic signal at shallow levels.