Anatomical and Microscopic Characteristics of Piper nigrum L. with Application in the Authentication of Commercial Ground Pepper Products

Adulteration and misidentification of botanical raw materials in herbal and spice products remain major concerns affecting product quality, safety, and therapeutic efficacy. This study investigated the anatomical and microscopic characteristics of Piper nigrum L. to establish reference data for the authentication of commercial ground pepper products. Anatomical investigations were performed using leaf epidermal peeling and paraffin-embedded transverse sections of stems, leaves, petioles, and fruits, while powder microscopy was conducted on authentic fruits and commercial ground pepper samples. Microscopic examination revealed that the adaxial leaf surface possessed tetracytic stomata, while the abaxial surface contained cyclocytic stomata, with prismatic calcium oxalate crystals and secretory cells also observed. The stomatal index averaged 20.20% per square mm², with guard cells measuring 5.38 µm in width and 27.63 µm in length on average. Glandular trichomes, two concentric vascular bundles, and starch granules were also identified. The micromorphology of ground pepper powder showed key components including epicarp, pericarp, parenchyma, sclereids, spiral vessels, and starch granules. The findings provided baseline pharmacognostic standards for raw material authentication and quality control of commercial herbal products. This anatomical data can also be integrated with molecular techniques or advanced image analysis to enhance the accuracy of product authentication in future studies. The results demonstrated that the anatomical and powder microscopic characters were reliable pharmacognostic markers for authentication, detection of adulteration, and quality control of commercial ground P. nigrum products.