Evolução das glândulas calicinais de Malpighiaceae: prospecções da anatomia floral no contexto da ordem Malpighiales

Abstract

The Malpighiaceae elaiophore were the first to appear in the evolutionary history of angiosperms and are usual features of the neotropical species of the family. Recognized by their floral morphology, Malpighiaceae exhibit flowers that are very similar to each other, with the most remarkable character the presence of pentamerous perianth with elaiophores in the calyx and the zygomorphic corolla. These characteristics have been maintained in different lineages of the family in response to the mutualistic relationship with oil-collecting bees. However, some neotropical lineages are eglandular and the processes by which their floral morphology has been modified are still unclear. Also, as the floral vasculature constitutes the most conserved part of a flower, studies of this type can elucidate stages before the current external morphology, as they show the flower's ancestral states. Thus, the main objective of this study was to understand, through floral vasculature, the evolutionary processes involved in the emergence, maintenance, and suppression of Malpighiaceae elaiophore considering the family circumscription in Malpighiales. Although they do not constitute floral organs themselves, the elaiophore remain as such, so that there are vascular traces in most eglandular lineages. Even though the floral morphology changes, including those with the actinomorphic corolla, derived eglandular species can still exhibit the same vascular pattern as basal lineages, confirming the vascular anatomy as the most conserved part of the flower, revealing its ancestral states. Comparative analyzes suggest that the eglandular calyx is homoplastic, as result of conation or reduction. Furthermore, floral anatomy proved to be relevant to understand the differences between Malpighiaceae and its sister group, Elatinaceae, revealing evidence about their reproductive system towards of autogamy. Data on the elaiophore vasculature and ontogenesis allow us to infer that their origin refers to the common ancestor of the Malpighiales, being relevant for the entire order too. Thus, Malpighiaceae is an excellent group of study to treat evolutionary aspects that modify floral morphology.