The reevaluation of Salacia lombardii (Celastraceae) based on phylogenetic position and biogeographic implications

Abstract

Biological inclusions preserved in the amber deposits from Chiapas, Mexico, provide evidence of a tropical environment at low latitudes in North America during the Miocene. Unfortunately, they have a scarce fossil record of plants, and most of them have been related to the extant taxa of the Neotropical region. However, this idea has not been evaluated through a phylogenetic context until now. Here, we analyzed the phylogenetic position of Salacia lombardii, a Miocene flower identified as an extinct species of Salacioideae (Celastraceae), which typically has flowers with a pentamerous perianth and trimerous androecium; nevertheless, a small set of taxa including S. lombardii have only two stamens. To evaluate the relationship between fossils with their potential near relatives, we used a combined matrix previously generated with molecular data combined with morphological characters from 6 genera and 28 species of Salacioideae through Parsimony and Bayesian criteria. The topologies of trees reported here are consistent with previous analyses for Salacioideae, recovering two clades: Neotropical and taxa with two-stamens. Salacia lombardii has an ambiguous position causing a polytomy in the strict consensus of Parsimony analysis. Nevertheless, there are only two alternative positions of the fossil in the MPTs (Most Parsimonious Trees): 1) as a sister group of Salacioideae or 2) as the sister group of clade from which Sarawakodendron and Salacioideae diverged. The latter is comparable with the tree of Bayesian analysis. Based on the criterion of topological congruence between Parsimony and Bayesian approaches, we support the second hypothesis, which suggests that Salacia lombardii occupies a transitional position between Salacioideae and Hippocrateoideae, as well as its close relationship with the Paleotropical region.