Morphoanatomical, Micromorphological, and Histochemical Characterization of the Vegetative Organs of Sida rhombifolia for Pharmacognostic Quality Control

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Sida rhombifolia L., Malvaceae, is widely distributed in tropical and subtropical regions and is frequently used in traditional medicine, although it is commonly regarded as a weed. Its identification is often compromised by morphological similarity among species of Sida and the widespread use of the vernacular name “guanxuma,” which may lead to taxonomic confusion and difficulties in pharmacognostic studies. This study characterizes the vegetative organs of S. rhombifolia by light microscopy, scanning electron microscopy, and histochemical assays to support pharmacognostic identification. Diagnostic anatomical and micromorphological features were investigated to support species identification and differentiation within the genus. Histochemical assays were also performed to determine the distribution of primary and secondary metabolites in plant tissues. The species exhibited a set of consistent diagnostic characters, including anisocytic and anomocytic stomata, dorsiventral mesophyll with mucilaginous and crystalliferous idioblasts, and non-glandular and glandular trichomes. Vascular and mechanical tissues showed well-developed lignified fibers, while the root and stem presented characteristic arrangements of vascular bundles and storage tissues. Histochemical analyses revealed the presence of lipids, phenolic compounds, alkaloids, mucilage, pectins, lignin, starch, and proteins, with specific tissue localization associated with functions of protection, secretion, support, and storage. The integration of anatomical, micromorphological, and histochemical data provides a robust pharmacobotanical framework for the identification of S. rhombifolia , supporting its differentiation from related species and contributing to taxonomic clarification within the genus Sida . These findings also provide valuable parameters for quality control of plant raw material and future pharmacological investigations.