Micromorphological and Histochemical Study of Senna martiana, a Medicinal Herb

Senna martiana (Benth.) H.S. Irwin & Barneby is endemic to Brazil's dryland Caatinga domain. The species is known as "canafistula" in folk medicine, and its leaves are used as a laxative. Anatomical and histochemical studies of the species' vegetative organs (roots, stems, and leaves) were conducted to identify features that would support its taxonomic classification, as well as provide quality control for its ethnomedicinal use. Dried fragments from both leaflet surfaces were examined using scanning electron microscopy, and paradermal and transverse sections were used in histochemical tests to confirm the presence of lipids, starch, alkaloids, and nonstructural phenolic compounds. Senna martiana exhibits a striate cuticle on both leaflet surfaces, with straight to curved anticlinal cell walls on the adaxial face and sinuous walls on the abaxial face. The leaflets are amphistomatic, with a variety of stomatal types (paracytic, anisocytic, and anomotetracytic). The midrib is plane-convex with a collateral vascular system; the petiole is elliptic with 6-8 vascular bundles; the leaf rachis is ovate with 4-5 vascular bundles. Stems have a siphonostelic ectophloic vascular system. Idioblasts containing crystal sand, prismatic crystals, druses, and starch grains were observed in all vegetative organs. The contour and number of vascular bundles in the petiole and rachis, along with the sclerenchyma bundles enclosing the vascular system or roots, were distinctive features for Senna martiana. These characters constitute an important support for species identification, differentiation, and quality control of its ethnomedicinal drugs.