Testing the monophyly of Aesculus L. and Billia Peyr., woody genera of tribe Hippocastaneae of the Sapindaceae.

Hippocastaneae is a well-supported clade in Sapindaceae that comprises 15+ species; 12+ in Aesculus , two in Billia , and one in Handeliodendron Rehder. The monophyly of Aesculus and Billia were widely assumed, but a recent molecular phylogenetic study of Sapindanceae used seven species of Aesculus and one each of Billia and Handeliodendron and showed that Billia and Handeliodendron were nested within Aesculus . Here, we tested the hypothesis that Aesculus and Billia are mutually monophyletic using phylogenetic analyses of seven molecular markers and 31 accessions of Hippocastaneae representing 14 species. We performed phylogenetic analyses using a dataset of concatenated genes as well as with coalescent method for constructing a species tree from individual gene trees. The analysis of seven concatenated markers and the species tree strongly supported the mutual monophyly of Aesculus and Billia . We also recovered support for the traditional arrangement of genera within Hippocastaneae: Aesculus and Billia comprising a clade that is sister to Handeliodendron . However, the relationships among the genera remain incompletely resolved. [ABSTRACT FROM AUTHOR]