Internal secretory structures and histochemistry in leaves of Baccharis notosergila Griseb. (Asteraceae, Astereae)

Baccharis notosergila Griseb. (Asteraceae, Astereae) is an aggressive weed of natural grasslands but it also has medicinal properties. The aim of this investigation was to increase the knowledge of internal secretory structure types and identify the main substances accumulated in them. Plants were collected in Buenos Aires province, Argentina. Vouchers were deposited in LPAG herbarium. Leaves were conserved in alcohol 70°. Leaves cross sections were obtained, others were made diaphanous, and all were stained with dyes and with reagents for histochemical analysis. False ducts (formed by cavities) and cavities themselves were found. The cavity itself is a short space, lined by short epithelial cells. False duct is a long and extended space lined by very long epithelial cells, developed from a row of elongated cavities during leaf growth. False ducts run on abaxial side along the major veins (1^st to 3^rd orders). Cavities are isolated or two-three clustered and located on lateral-abaxial side from 1^st to 5^th order veins, at the end of veinlets (6^th order) and in mesophyll. Both structures are enclosed by parenchyma sheath. The chemical compounds (resins, phenolic and lipophilic compounds) accumulated in cavities and false ducts can have multiple applications, either for their medicinal properties or might be used for the biocontrol of pathogens to improve sustainable agricultural systems.