Phylogenetics of the supertribe Paulliniodae (Sapindaceae) with emphasis on chromosome evolution: Taxonomic implications including the new genus Acevedoa.

Abstract

Background and aims: The supertribe Paulliniodae includes Athyaneae, Bridgesieae, Thouinieae, and Paullinieae tribes. Molecular phylogeny and chromosomal diversity are relatively known, and some doubts persist about chromosome evolution processes and the taxonomic position of a group of Cardiospermum and Urvillea species weakly associated with Serjania.

Methods: We analysed the molecular phylogeny and diversification time of the group, including unpublished DNA sequences of the ITS, trnL intron and trnL-trnF for 26 species. A total of 87 species were subjected to maximum likelihood and Bayesian analysis of molecular sequences. The association between chromosome number variation and phylogenetic relationships was analysed using ChromEvol, incorporating 14 newly determined chromosome numbers for Athyana, Paullinia, Serjania, and Urvillea.

Key results: The basic chromosome number reconstructions in Paulliniodae indicated x = 15 in all models. These results demonstrate a significant chromosome reduction process in the tribe Paullinieae that allows characterising some genera of the tribe during the late Oligocene/early Miocene (15-20 Mya), supporting the foundation of a new genus to accommodate Cardiospermum integerrimum and C. heringeri, two species with uncertain taxonomy position.

Conclusion: We propose the new genus, Acevedoa, which is defined by a unique set of character states, including two corniculiform nectaries, in the form of arched horns, calyx pentamerous, fruit trigonous turbinate, 3 winged, with remarkable stipe, relatively large sculptured seeds, and 2n = 14. The following two new combinations are made to incorporate the results of our findings: Acevedoa heringeri and A. integerrima. Descriptions and illustrations are provided, with comments on geographical distribution, phenology, conservation status, and generic relationships. The lectotype for the name belonging to Cardiospermum integerrimum is designated. A key to the genera of Paullinieae is added. The new genus, supported by morphological, chromosomal, and molecular evidence, adds new features and extends knowledge on the supertribe Paulliniodae.