Caracterização microscópica de cristais de Baccharis (Asteraceae): uma contribuição para a diferenciação das espécies

Abstract

The presence of inorganic crystals in plants is very common, being found mainly in the form of calcium oxalate. There are several functions attributed to the production of crystals, from the ionic balance maintenance, protection against herbivores and even support and rigidity of tissues. Crystals can vary considerably in shape and location from species-specific, suggesting that they go through genetic control, thus constituting species identification and classification characters. Thus, the present work aimed to analyze about 10% of Baccharis species (44 species) in order to differentiate them through the presence, morphology and chemical composition of the crystals, providing pharmacobotanical subsidies for the differentiation and identification of these species. Analyses were performed by polarized light microscopy, scanning electron microscope with emission gun (SEM-FEG), x-ray energy dispersive system (EDS) and RAMAN spectroscopy. Among the species analyzed, 42 presented crystals bipyramidal, cuneiform, arrow, styloid, druses, pyramidal, tabular and crystals sands, as well as forms not yet described in the literature, such as gyrohedral, prismatic trigonal and crystals sand butterfly-tie typ. In general, each species presented a specific subset of crystals, allowing the differentiation of the species. Some sections of the genus presented a crystalline pattern, such as Aphyllae, Angustifoliae, Oblongifoliae, Racemosae, Canecentes, Agglomeratae and Tarchonanthoides, where the species included in each section showed at least a similar crystalline morphotype for that section. The analyses of EDS showed peaks of calcium, carbon and oxygen, indicating the chemical composition of calcium oxalate, while the RAMAN spectroscopy demonstrated the presence of crystals, both monohydrate, observed in crystals considered of the monocyclic system, such as styloids, and dihydrate, observed in crystals of the tetragonal system, such as bipyramidal crystals. It was verified that the set of crystalline morphotypes present in the Baccharis species allow the differentiation and identification of the analyzed species, demonstrating importance for taxonomy and for the diagnosis of plant drugs.