Micromorphological and histochemical analysis of the medicinal herb
Senna martiana using light and scanning electron microscopy
Abstract
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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,
anomotetracytic, and brachyparacytic). 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 distinctive combination of
leaflet edge contours, leaf rachis and stem structure, and the
arrangement and number of vascular bundles provides a set of
distinguishing features for Senna martiana that are useful for
both taxonomy and quality control of its ethnomedicinal use.