African Sesuvium Systematics

Sesuvium (Sesuvioideae-Aizoaceae) comprises leaf succulent annual and perennial herbs distributed in coastal or saline sites of subtropical and tropical regions. Some species of the genus tolerate highly salinized or polluted soils and show soil-improving properties. Sesuvium shows high flexibility of photosynthetic types, including and integrating C3, C4, and CAM photosynthesis. Previous molecular phylogenetic studies failed to resolve the infrageneric relationships of the genus. However, a better understanding of the systematics of this group is a prerequisite for further evolutionary studies. We explored the suitability of genome skimming, including mainly herbarium material, to produce a robust phylogeny of the presumably young African clade of Sesuvium. The approach generated an average of 6,289 orthologs per genome skimming sample and 30 complete to mostly complete plastomes. The coalescent-based species tree, as well as the plastome tree, shows stable resolution at the backbone of the African Sesuvium clade. An annual C3 species, here newly described, is sister to a C4 clade that is subdivided into two subclades, one comprising the annual S. hydaspicum (incl. S. nyasicum) and the other three perennial species, S. crithmoides, S. congense, and S. sesuvioides. Within each of these two subclades, high gene tree discordance, mainly driven by gene tree estimation error, was found.