、SECRETORY STRUCTURES IN LEAVES AND FLOWERS OF TWO DRAGON'S BLOOD CROTON (EUPHORBIACEAE): NEW EVIDENCE AND INTERPRETATIONS

摘要

Premise of research. Previous studies of secretory structures in species of the Neotropical dragon's blood Croton (section Cyclostigma) show inconsistencies in their classification. An accurate assessment of the identity and homology of such structures is essential for taxonomic and evolutionary studies. Methodology. Field-collected leaves, stipules, and flowers at different developmental stages were sampled. The material was subjected to standard anatomical study by light microscopy and SEM, and secretions were evaluated by histochemical analyses. Pivotal results. Leaves and flowers of Croton echinocarpus and Croton urucurana present five secretory structures (idioblasts, laticifers, colleters, extrafloral nectaries, and floral nectaries) with high similarity between the two species. Idioblasts secrete compounds of a mixed nature; laticifers are branched and nonarticulated; and colleters and nectaries present hydrophilic secretion. The leaf marginal glands previously described as extra-floral nectaries are actually colleters of the standard type. We found colleters in staminate and pistillate flowers. The histochemical tests detected proteins in the secretions of all structures. Conclusions. The classes of secondary metabolites detected support the biological activities of secretion described in the literature. The correct identification of colleters in flowers establishes a new register of these structures in flowers of this genus. We show that an approach integrating anatomic structure, histochemistry, and period of secretion activity allows for a more accurate classification and homology assessment of secretory elements in this genus, which is exceptionally rich in this type of structures.