Abstract

Variable rates of molecular evolution have been documented across the tree of life, but the cause of this observed variation within and among clades remains uncertain. In plants, it has been suggested that life history traits are correlated with the rate of molecular evolution, but previous studies have yielded conflicting results. Exceptionally large phylogenies of five major angiosperm clades demonstrate that rates of molecular evolution are consistently low in trees and shrubs, with relatively long generation times, as compared with related herbaceous plants, which generally have shorter generation times. Herbs show much higher rates of molecular change but also much higher variance in rates. Correlates of life history attributes have long been of interest to biologists, and our results demonstrate how changes in the rate of molecular evolution that are linked to life history traits can affect measurements of the tempo of evolution as well as our ability to identify and conserve biodiversity.