Leaf form–climate relationships on the global stage: an ensemble of characters

Abstract Aim Early in their evolution, angiosperms evolved a diversity of leaf form far greater than that of any other group of land plants. Some of this diversity evolved in response to varying climate. Our aim is to test the global relationship between leaf form in woody dicot angiosperms and the climate in which they live. Location We have compiled a data set describing leaf form (using 31 standardized categorical characters) from 378 natural or naturalized vegetation sites from around the world. Our data include sites from all continents except A ntarctica and encompass biomes from tropical to taiga, over a range of elevations from 0.5 m to over 3000 m. Methods We chose the C limate L eaf A nalysis M ultivariate P rogram sampling, scoring and analytical protocols to test the relationships between climate and leaf form, which is based on canonical correspondence analysis. Cluster analysis evaluates the role of historical factors in shaping the patterns, and pairwise Pearson correlations examine the relationships among leaf characters. Results Woody dicot leaf characters form a physiognomic spectrum that reflects local climate conditions. On a global scale, correlations between leaf form and climate are consistent, irrespective of climate regime, vegetation type or biogeographic history. Relationships with temperature variables are maintained even when leaf margin characters, regarded as being particularly well correlated with mean annual temperature, are removed. Main conclusions In natural woody dicot vegetation an integrated spectrum of leaf form has developed across multiple leaf character states and species. This spectrum appears more strongly influenced by prevailing climate than biogeographic history. The covariation of leaf traits across species suggests strong integration of leaf form. New methods of exploring structure in multidimensional physiognomic space enable better application of leaf form to palaeoclimate reconstruction.