Morphoanatomy and histochemistry of Baccharis palustris: insights into a highly endangered endemic species from Southeastern America

Abstract

Morphoanatomy and histochemistry of Baccharis palustris: insights into a highly endangered endemic species from Southeastern America. The phenotypic plasticity of the Baccharis genus makes species identification difficult, even at the flowering stage. In this context, morphoanatomical studies are a powerful tool for botanical authentication, mainly emphasizing the recognition of diagnostic characteristics that may be useful for distinguishing similar species. Given the limited knowledge available about the endemic species B. palustris, this work aimed to characterize the morphoanatomy and histochemistry of its vegetative aerial parts to identify characters with diagnostic value and to elucidate the sites of synthesis and accumulation of metabolites of medicinal importance. B. palustris leaf showed pinnate, camptodrome-brochidodrome venation patterns. Blade with dorsiventral mesophyll, aerenchymatous spongy parenchyma, collateral vascular bundles, and different types of stomata and trichomes, including glandular trichomes with a multi-layered base evidenced and described for the first time in the genus. The petiole was winged, with three collateral vascular bundles. The stem showed a penta-lobulated contour with unusual growth, starch, and crystals in the pith. The presence of secretory ducts and glandular trichomes, which synthesized lipids, terpenes/polyacetylenes, and phenolic compounds, was observed. The morphological/histochemical characteristics described in this work contribute to the knowledge of the species, highlighting the importance of its preservation as a valuable resource.