Leaves adapt to the physical conditions of their environments which include temperature, precipitation, atmospheric CO2 concentrations, and light levels. For instance, to maximize energy conservation, they tend to be smaller in cooler and drier habitats with condensed venation and toothed margins. Conversely, leaves tend to be larger under warmer and wetter conditions and have ‘drip tips’ and entire margins. Such characteristics are preserved in the plant fossil records and can be used to infer local conditions when the plants were alive. During the early Paleogene, Earth had a very warm global climate and there were no ice sheets on the poles. This interval had several rapid warming events, including hyperthermals, the most prominent being the Paleocene-Eocene Thermal Maximum and the long-term warming event culminating at the Early Eocene Climatic Optimum (~53 million years ago). These warming events coincided with increased atmospheric CO2 levels, changes in weathering patterns, and resulted in changes in the composition of plant communities and possibly in their diversification rate. This project focuses on understanding plant communities from the early Paleogene of the Gulf Coastal Plain using fossil leaves collected from Eocene deposits in Tennessee and Kentucky. A systematic census collection will base our analyses on the Manual Leaf of Architecture, leaf physiognomic traits, and cuticular morphology and further apply these methods to at least three systematic censuses of flora. Our ultimate goal is to understand what communities prefer specific environmental conditions in order to better predict the effects of global warming on plant communities.