Evolution of leaf blade anatomy in Allium (Amaryllidaceae) subgenus Amerallium with a focus on the North American species

• Premise of the study: Reconstructing ancestral states is a useful method to understand the pathway and patterns of character evolution and to test specific hypotheses within a phylogenetic context. Using a phylogenetic hypothesis of the subgenus Amerallium and related subgenera based on molecular data, we reconstructed the evolutionary history of leaf blade anatomical characters and identified those characters that are most congruent with phylogenetic relationships. Furthermore, we used these character histories to investigate the evolution of terete leaves and explore a possible correlation between environment and leaf anatomy in the North American species. • Methods: Sixty‐seven North American and Old World species were sampled from all major infrageneric taxa and lineages for transectional leaf anatomy. To provide a phylogenetic framework for interpretation, representatives of Old World Amerallium and related subgenera were added to a published data matrix of North American taxa and ITS, ETS, trnL – F , and rpL32 – trnL sequences. • Key results: Four anatomical characters, namely leaf‐blade shape in transection, presence versus absence of palisade mesophyll, distribution and orientation of vascular bundles, and position of laticifer cells, were found to be congruent with phylogenetic relationships and useful diagnostic traits within North American species. Character reconstructions show that terete leaves in North American species evolved from flattened leaves via a possible transition from subterete to terete leaves. Furthermore, terete leaves possess traits that are indicative of possible adaptation to xeric environments. • Conclusions: The findings from this study provide valuable information for understanding the evolution of leaf‐blade anatomy in North American Allium species.