Variability of Cinnamomum (Lauraceae) Leaf Architecture in Relation to Climatic and Historical Constraints: Implications for Paleoclimatic Studies

Abstract : Premise of research. Fossil leaves are commonly used as proxies for continental paleoclimate reconstruction. In particular, temperature and precipitation variables are derived from taxon-free methods using only fossil leaf morphology. Although there is a general relationship between leaf form and climate at a global scale, possible differences between and within angiosperm families remain little explored. Methodology. In this article, we analyzed the influence of phylogenetic relatedness and climate on leaf architecture in 30 species of Cinnamomum (Lauraceae). Nineteen morphological features were selected and documented on the basis of digitized herbarium specimens. Repeatability was measured for all traits. Phylogenetic signal was measured using Blomberg’s K. The relationship between morphological variables and climatic variables was investigated using univariate and multivariate statistical approaches. Pivotal results. Our analysis revealed that phylogenetic signal was mainly observed in traits linked to the venation pattern. Size- and shape-related variables are more influenced by climatic parameters than by historical constraints. Cinnamomum leaf morphology is significantly correlated with mean annual temperature and temperature seasonality. Conclusions. Shape and size are representative of convergent temperature-related characters in this genus. Our analysis validates the use of this genus for taxon-free paleoclimatic reconstruction methods relying on such data. The absence of phylogenetic signal in size- and shape-related traits contrasts with earlier studies on distantly related taxa and confirms that historical constraint on leaf morphology is variable among families.