The evolutionary history of Senna ser. Aphyllae (Leguminosae–Caesalpinioideae), an endemic clade of southern South America

ROBBIATI, FEDERICO O.; MARAZZI, BRIGITTE; ANTON, ANA; VÁSQUEZ-CRUZ, MARILYN; FORTUNATO, RENÉE H.

PLANT SYSTEMATICS AND EVOLUTION

SPRINGER WIEN

Año: 2017

0378-2697

In the legume genus Senna, series Aphyllaeincludes seven species of leafless shrubs and subshrubsfrom arid, semiarid and xerophilous areas of three differentbiogeographic subregions in southern South America.In this study, we investigated the evolutionary historyof Aphyllae in a molecular phylogenetic framework. Wereconstructed phylogenetic relationships among Aphyllaespecies based on DNA sequence data of four plastid(rpS16, rpL16, matK, trnL-F) and one nuclear (ITS) regionfrom 23 accessions, analyzed with parsimony, Bayesianand maximum likelihood methods. We inferred the evolutionaryand biogeographic history estimating divergencetimes and reconstructing ancestral character states and ancestral areas of distribution. Series Aphyllae was foundto be monophyletic, and the taxa formed two main clades:Clade A gathering S. aphylla var. aphylla, S. crassiramea,S. rigidicaulis and S. spiniflora; and Clade B grouping S.acanthoclada, S. aphylla var. divaricata, S. aphylla var.pendula and S. pachyrrhiza. The morphologically complexS. aphylla appears thus polyphyletic. Molecular datingand ancestral area reconstructions suggest that the Aphyllaeclade started to diversify in the South American TransitionZone in the Late Pliocene. Based on these results, wehypothesize that this diversification occurred during thelast period of Andean uplift with the aridification in SouthAmerica. The ancestral character state reconstructions suggestthat, in addition to the loss of leaves in adult plants,series Aphyllae evolved various morphological features,such as fastigiate, thickened or decumbent?subdecumbentbranches during the colonization and establishment in differentarid and semiarid lands in South America.