Pulsed evolution shaped extant angiosperm pollen disparity.

Abstract

Pollen grains, the male gametophyte of seed plants, are enclosed within sporopollenin walls that yield remarkable structural diversity and exceptional preservation, making them invaluable proxies for past plant diversity. Despite their importance, the diversification patterns of angiosperm pollen are not well quantified or understood. By integrating a genus-level pollen trait dataset with a time-calibrated phylogeny, we quantified the evolutionary dynamics of angiosperm pollen, including its morphospace occupation, disparity, and rates of morphological evolution. Our results reveal that angiosperm pollen disparity expanded through two major pulsed increases during the Mid Cretaceous and Paleogene periods marked by significant environmental shifts and correlated with key pollen innovations. These findings are robust under varying hypotheses of crown angiosperm age and highlight a synergistic interplay between evolutionary innovation and key ecological opportunities, rather than a singular early burst of diversification. Based on inferences from extant morphologies, our results show that the initially low disparity in early angiosperm evolution was followed by a rapid Mid Cretaceous surge, providing critical context for interpreting patterns observed in the angiosperm fossil record. These results underscore the power of pollen disparity in tracing angiosperm radiation and understanding the diversification of Earth's multicellular life.