Functional and historical drivers of leaf shape evolution in Palms (Arecaceae)

Aim Leaves display a remarkable variety of shapes, each with potential ecological advantages in specific climates. While relations between leaf shape and either climate or height has been relatively well studied in eudicots, the macroecological drivers of shape remain poorly known in monocots. Here, we investigated associations between climate and plant height with the evolution of leaf shape in a clade with high species and morphological diversity. Location Global. Time period Cretaceous to contemporary. Major taxa studied Palms (Arecaceae). Methods We apply a Bayesian phylogenetic mixed model to test for associations between climate and leaf shape (all entire-leaved, pinnate-dissected, palmate-dissected, and costapalmate). We further reconstruct the ancestral leaf shape using multistate speciation and extinction models and compare the frequency of shapes with global temperatures through time. Results We find that plant height associates with dissected leaves and that annual precipitation associates with pinnate shapes. The ancestral leaf shape is unclear but early diversification was dominated by pinnate-dissected palms, which has remained the most species-rich form of leaves throughout palm history. Main conclusions Palms that are tall and live in humid regions are more likely to have pinnate leaves. Through geological time scales, temperature did not play an obvious role in determining leaf shapes. This study contributes to our understanding of how the diversity of leaf shapes is linked to biological and climatic factors.