NERC/NSF Mind the Gap: Tackling the Molecule - Fossil Divide in Angiosperm Evolution Using Fossil Pollen, Superresolution Microscopy, and Deep Learning

Most of the plants on Earth – around 374,000 species – are flowering plants, also known as angiosperms. The appearance of angiosperms and their diversification changed the planet in important ways. Understanding the history of how angiosperms evolved is key to explaining how they became so widespread and diverse. However, we still do not fully understand when or how angiosperms began to diversify, which prevents us from determining what caused their rapid spread. Studies using molecular data show that flowering plants may have evolved much earlier than the first fossil evidence indicates. This project aims to bridge the divide between molecular studies and fossils by focusing on the pollen records of the Chloranthaceae. The Chloranthaceae comprise a flowering plant family that includes some of the oldest angiosperm fossils. The project will use advanced techniques like optical superresolution microscopy, deep learning, and new methods for reconstructing evolutionary trees. It will train two postdoctoral researchers in these cutting-edge biological and computer science methods. In addition, the project will work with non-profit groups and the UK Open University’s OpenLearn platform to offer free online educational materials about the evolution of flowering plants to the global community. This study will build a new phylogenomic tree for Chloranthaceae and use phylogenetically-informed deep learning models to place Chloranthaceae fossils within this new phylogeny. Placing fossils within the phylogeny will establish the timing of diversification within the plant family and whether Early Cretaceous (125 million years ago) Chloranthaceae pollen, which are the earliest fossil evidence for this group, represent early- or late-diverging species. If the fossils represent early-diverging species, this will support an Early Cretaceous origin for the Chloranthaceae. If the fossils represent late-diverging species, this will support a much older origination date in line with molecular estimates. Establishing the age of Chloranthaceae will also help resolve the timing of diversification of early angiosperms more broadly by constraining the ages of lineages at the base of the angiosperm phylogeny and will address the debate on when the first flowering plants appeared. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.