Phylogenomic insight into dysploidy, speciation, and plastome evolution of a small Mediterranean genus Reichardia (Cichorieae; Asteraceae)

Reichardia Roth is a small Mediterranean genus comprising ten homogeneous species with basic chromosome numbers of 7, 8, and 9. To assess the plastid genome evolution and differentiation of Reichardia species, we assembled the complete plastome sequences of seven Reichardia and two Launaea species and conducted various phylogenomic analyses comparatively with nuclear ribosomal DNA ITS sequences. Reichardia and Launaea plastomes were highly conserved in gene content and order, containing 130 genes. Plastid phylogenomic reconstruction strongly suggested that Reichardia was a sister to Launaea, and its common ancestor initially diverged into two major lineages: the first containing species with n = 8 chromosomes exclusively, and the other with n = 9, 8, and 7 chromosomes. Although the ancestral Reichardia karyotype was suggested to most likely be n =9 from ancestral chromosome number reconstruction, the pattern of descending dysploidy indicated by the phylogenetic trees based on nuclear ribosomal DNA ITS was less evident in the trees based on the plastome. Possible reasons for these findings are discussed.

Automated summary

This study investigated the plastid genome evolution and differentiation of Reichardia species through phylogenomic analyses. The plastomes of Reichardia and Launaea were highly conserved in gene content and order, and Reichardia was found to be a sister species to Launaea with two major lineages. However, the pattern of descending dysploidy observed in the nuclear ribosomal DNA ITS-based phylogenetic trees was less evident in the plastome-based trees.