I explore how plants can be used to reconstruct ancient environments, and the (paleo-) physiological underpinnings behind these plant-environment relationships. Recent and current projects include the reconstruction of paleo-atmospheric carbon dioxide levels from the stomatal distributions in plant leaves, and the development of mechanistically-grounded proxies for climate and leaf ecology from the size and shape of fossil leaves. I also compile ancient carbon dioxide records and investigate the strength of carbon dioxide-temperature coupling over multi-million-year timescales.