Assessing the relationship between climate and Cyathea cooperi physiognomy

It has been known for over a century that leaf shape characteristics correlate significantly with climate. In regions with colder, wetter climates, there are generally more leaves with serrated margins, or teeth. Using this information, paleobotanists can estimate the paleoclimate from the shapes of fossil leaves. Up until now, these correlations have only been calibrated for angiosperm leaves. Expanding this tool to include evolutionarily more ancient plant groups would allow paleobotanists to better estimate terrestrial climates further back in Earth history. Prior to this study, very little work has been done on the connection between tree fern physiognomy and climate. Tree ferns are found in the fossil record nearly twice as far back in Earth history as angiosperms (~300 million years). Here, I examined the correlation between leaf shape characteristics of Cyathea cooperi, a tree fern native to Queensland, Australia, and yearly temperature and precipitation. It found significant correlations between tree fern physiognomy and climate. C. cooperi tooth abundance and size correlates significantly with both mean annual temperature and mean annual precipitation. Given the correlation values, it would appear the water availability drives tree fern physiognomy more so than does temperature. The results were also compared to a similar study of Puerto Rican tree fern Cyathea arborea, which helped to confirm these connections. Ultimately, this study could be useful for establishing a tool to reconstruct paleoclimates using tree ferns.