The rise and fall of Sauropus (Phyllanthaceae) : a molecular phylogenetic analysis of Sauropus and allies

Molecular phylogenetic studies focused on the genus Phyllanthus L. (Phyllanthaceae) showed that Sauropus Blume (including Synostemon F.Muell.) and its related genera Breynia J.R.Forst. & G.Forst. and Glochidion J.R.Forst. & G.Forst. should be united with Phyllanthus to create a monophyletic genus. The relationships within Sauropus and its relationship with Breynia were studied to test/corroborate such a broad definition of Phyllanthus. The molecular phylogenetic analyses show that Sauropus in the broad sense is composed of two distinct groups, the former Australian Synostemon and the Southeast Asian Sauropus in the strict sense with the monophyletic Breynia embedded in the latter. As the phylogeny of the species rich Phyllanthus is still far from completed and the results here strongly support the distinction of monophyletic groups such as Glochidion, former Synostemon, and Sauropus/Breynia. These genera are recognisable, while union with Phyllanthus (suggested by Hoffmann and co-authors in 2006) will turn the latter into an unrecognisable monolithic giant of a genus. It is a much better strategy to use the complete phylogeny of Phyllanthus to render it into smaller, monophyletic genera that can be characterized. The present study shows Synostemon has to be recognised again on generic level. Breynia, the older name, is nested within Sauropus, leading us to transfer the latter to Breynia. Within this broadened Breynia, two subgenera and two sections are distinguished, subgenus Sauropus and subgenus Breynia with section Cryptogynium and section Breynia under the latter