Secretory Structures in Vegetative Organs of Leguminosae: A Review of Subfamilies Caesalpinioideae, Cercidoideae and Detarioideae

Abstract Leguminosae comprises approximately 19,325 species in 727 genera, organized into six subfamilies. Its occurrence is notable in all Brazilian phytogeographic domains, which integrates the third largest angiosperm family and the second in economic importance. Species of Leguminosae present several secretory structures that are used as taxonomic markers and exudated considered important for ecological interactions. This study aimed to review the types of secretory structures, distribution, and chemical composition of the secretions of Caesalpinioideae (including the Mimosoid clade), Cercidoideae, and Detarioideae subfamilies of Brazilian genera, as well as to evaluate the circumscription of the Mimosoid clade within the subfamily Caesalpinioideae based on these structures. A review was performed by compiling information from specialized journals and repositories of articles, dissertations and theses related to different secretory structures in the three subfamilies. Secretory structures were found in 242 species — 224 from Caesalpinioideae, 7 from Cercidoideae, and 11 from Detarioideae. Extrafloral nectaries predominated in 177 species, followed by colleters in 54 species, idioblasts in 15 and secretory cavities in eight of them. Caesalpinioideae shows primary metabolites associated with secretory structures, which enhance mutualistic interactions. The mucilage present in colleters protects the shoot apex against desiccation. The terpenoid and flavonoid classes are mostly produced by these distinct secretory structures in Cercidoideae and Detarioideae. Of the secretory structures found, a predominance of extrafloral nectaries was observed in both the Mimosoid clade and among the studied Caesalpinioideae genera. This study supports the circumscription of the Mimosoid clade and offers important information for future systematic and evolutionary studies within Leguminosae.