Invasion of the South American dry diagonal: What can the leaf anatomy of Pitcairnioideae (Bromeliaceae) tell us about it?

The current circumscription of Pitcairnioideae (Bromeliaceae) comprises the genera Deuterocohnia, Dyckia, Encholirium, Fosterella, and Pitcairnia. The leaf anatomy in Bromeliaceae provides interesting features that have helped to resolve taxonomic problems and can reveal several adaptations to the environment. We combined information on the leaf anatomy of 114 species of the five genera of this family with a phylogenetic approach to the Pitcairnioideae, seeking micromorphological synapomorphies that could aid in the recognition of each clade, in addition to tracing its evolutionary history. Through this analysis it was possible to identify characteristics that distinguish a xeric clade and mesic genera. As a general pattern, each main cladogenic event in Pitcairnioideae is marked with an anatomical synapormorphy. The presence of xeric synapomorphies (especially CAM, fibrous hypodermis, and ad- and abaxial aquiferous parenchyma) apparently played an essential role in allowing species of Deuterocohnia, Dyckia, and Encholirium to occupy the South American dry-diagonal.