Historical biogeography and character-mapping of Acridocarpus (Malpighiaceae) evidence a revised infrageneric classification system and shifts in African biomes from the Eocene to the Miocene

Abstract

Background and aims – Acridocarpus belongs to one of the seven Malpighiaceae lineages that dispersed from the Neotropics to the Paleotropical region, being by far the most widely diversified and distributed genus of the family in Africa. In this study, we tested the monophyly and validity of the current infrageneric classification of Acridocarpus with a dated molecular phylogeny. We also reconstructed ancestral range distributions for biomes and continents to elucidate which route led to the colonisation of Africa by the most recent common ancestor (MRCA) of this genus.

Material and methods – We sampled six genes (ITS, PHYC, matK, ndhF, rbcL, and trnL-F), 21 species of Acridocarpus, and three outgroup species to test the monophyly of the infrageneric classification of the genus. BI and ML analyses were performed for the combined molecular dataset. A total of 20 morphological characters were optimised on the tree.

Calibration points derived from a published Malpighiaceae chronogram were used for a dating analysis. Ancestral areas of Acridocarpus and its relatives were estimated for continental (South America, Africa, India, Madagascar, and New Caledonia) and biome (dry forests, humid forests, and savannas) ranges. Key results – The pre-existing infrageneric classification of Acridocarpus was recovered as non-monophyletic due to being solely based on homoplastic morphological characters.

The MRCA of Acridocarpus colonised rainforests of East Africa + Madagascar 43 Mya via the Gondwana route and greatly diversified in this region, with a single long-distance dispersal event from Madagascar to New Caledonia (Oceania). The genus colonised African dry forests at least four different times, starting in the Oligocene and diversified a single time in Malagasy savannas in the Miocene.