A new research paper in the Proceedings of the National Academy of Science reveals that the lineage to which one third of the estimated 300,000+ modern-day flowering plant species belong, including most trees, experienced a burst of rapid diversification about 90 million years ago, which in turn set the stage for the quick radiation of amphibians, ants, placental mammals and ferns. The study, based on an analysis of DNA from living samples, shows the evolutionary relationships of these plants and provides evidence for their rapid emergence and diversification.

The findings provide a picture of one of several bursts in diversification that shaped the evolution of flowering plants (angiosperms) and created the angiosperm-dominated forests that ultimately provided habitat for many of the world’s organisms. The study focused on the rosid clade, the first big group of angiospermss to be evaluated using a rigorous dating process that combines gene sequencing with calibration against the fossil record.

Prior to this study, a phylogenetic tree—a sort of family tree—based on molecular data from three genes had been constructed. But the evolutionary burst that created the rosid clade occurred so quickly that more genetic information was needed to understand better how species within the clade were related and when the divergences happened. Using a phylogenetic tree to date the diversification of lineages requires the use of a molecular clock. To compensate for the frailties of a strict molecular clock, the study used algorithms that accommodate the different rates of evolution among the different groups within the rosid clade. Well-understood and confidently dated rosid fossils have been selected to help calibrate that clock by setting minimum ages for member species.

The first author, Hengchang Wang, currently with Wuhan Botanical Garden, the Chinese Academy of Science, is a postdoctorial scientist of University of Florida. The work has been achieved collaborately by other authors from Oberlin College, University of New Orleans, and Harvard University.