Plant range size (geographic area occupied by a species), a key predictor of species’ extinction risk, is shaped by an interplay of evolutionary and ecological processes. Yet understanding how species’ biological traits interact with environmental factors to determine range size remains challenging. I hypothesize that plant trait flexibility (ability of traits to evolve to different trait states) and genome size (total DNA in cell’s nucleus) are two key biological factors that influence range size. Genome size imposes biophysical constraints on cell size and rate-related cellular traits (like cell cycle duration) impacting functional traits, e.g., photosynthetic rate, seed size. Large-genomed lineages with stronger biophysical constraints, are predicted to exhibit slower trait evolution compared to small-genomed lineages that, at the whole plant level, can impact where they can and cannot grow. High nutrient demand of large-genomes can also restrict species’ range size in nutrient-poor conditions. But it remains unclear how genome size’s effects on trait flexibility and diversification, influenced by abiotic factors, impact range size. I will address this knowledge gap by establishing a single quantitative framework using the widely distributed palm family (Arecaceae) as a model system. Palms possesses considerable genome size and trait diversity. A major methodological challenge of obtaining genome size data will be addressed by developing a method to predict genome size from leaf stomatal guard cell size. With a secondment and collaborating with a team of leading experts, I will expand my expertise on cytogenetics and evolution while acquiring new skills on ecological analyses, and develop my supervisory and leadership skills. Together, this project will lay the foundations for my future role as an independent group leader in plant evolutionary ecology with a focus on cytogenetics, to aid in conservation efforts.