A rich fossil record yields calibrated phylogeny for Acanthaceae (Lamiales) and evidence for marked biases in timing and directionality of intercontinental disjunctions

More than a decade of phylogenetic research has yielded a well-sampled, strongly supported hypothesis of relationships within the large (> 4,000 species) plant family Acanthaceae. This hypothesis points to intriguing biogeographic patterns and asymmetries in sister clade diversity but, absent a time-calibrated estimate for this evolutionary history, these patterns have remained unexplored. Here, we reconstruct divergence times within Acanthaceae using fossils as calibration points, experimenting both with fossil selection and effects of invoking a maximum age prior related to the origin of Eudicots. Contrary to earlier reports of a paucity of fossils of Lamiales (an order of ~23,000 species that includes Acanthaceae) and to the expectation that a largely herbaceous to soft-wooded and tropical lineages would have few fossils, we recovered 51 reports of fossil Acanthaceae. Rigorous evaluation of these for accurate identification, quality of age assessment, and utility in dating yielded...