Evolution in the plant kingdom is marked by the successive origin of new forms, including the land plants, tracheophytes, seed plants, and flowering plants. The origin of each form was followed by a period of remarkable innovation and diversification, leading to the establishment of the modern land flora. Work in the Mathews lab focuses on plant phylogeny and on discovering mechanisms of diversification. We use the phytochrome system as a source of DNA sequence data from which to infer evolutionary trees and also to investigate how proteins change through evolutionary time and in plants with different life histories. These studies lay the groundwork to address the question of how changes in light-sensing molecules have influenced the ability of plants to survive and diversify.