TIME TREE OF RUBIACEAE: PHYLOGENY AND DATING THE FAMILY, SUBFAMILIES, AND TRIBES

Rubiaceae are one of the largest families of plants, with; 13,000 species. In this study, we have estimated the phylogeny for 534 Rubiaceae taxa from 329 genera with up to five different chloroplast regions by Bayesian analysis. It resulted in a highly resolved tree with many strongly supported nodes. There is strong support for the three subfamilies (Cinchonoideae, Ixoroideae, Rubioideae) and most of the 44 included tribes. A scaled-down data set of 173 Rubiaceae taxa was used with a Bayesian approach to estimate divergence times for clades classified as tribes and subfamilies. Four fossils were used as minimum age priors, one inside each subfamily and one for Rubiaceae as a whole (Faramea-type pollen, Scyphiphora pollen, Cephalanthus pusillus fruits, and Paleorubiaceophyllum eocenicum leaves). The estimated lineage (stem) divergence time for Rubiaceae is 90.4 Ma. The estimated lineage divergence times for the subfamilies are 84.4 (86.6) Ma for Rubioideae, 73.1 Ma for Ixoroideae, and 73.1 Ma for Cinchonoideae. The estimated lineage divergence times for the tribes vary between 86.6 and 14.2 Ma. Classification, relationships, geographical distribution, and age estimates are presented and discussed for all tribes.