Morphological and Anatomical Characterization of the Endemic Onosma vanensis Fırat & Binzet from Türkiye

Abstract

Onosma vanensis is an endemic species from Türkiye, and this study presents a detailed investigation of its anatomical features based on specimens collected from a newly recorded population in Muş province. Root, stem, and leaf tissues were examined using light microscopy to characterize the anatomical structure of the species. The roots display a well-developed secondary structure, in which the pith is entirely composed of tracheary elements and extensive xylem occupies a major portion of the cross-section. The stem has a uniseriate epidermis covered with setose and glandular trichomes, a 7–8 layered cortex, and a distinct vascular system with a 2–3 layered cambium. Leaves are isobilateral and amphistomatic, consisting of a uniseriate epidermis on both surfaces covered by a thin cuticle. The mesophyll thickness ranges between 234.5–328.8 µm, comprising 2(–3) layers of palisade parenchyma beneath the upper epidermis, a single palisade layer above the lower epidermis, and 3–4 layers of spongy parenchyma. Stomata are anomocytic to anisocytic, located at the same level as epidermal cells, and present on both leaf surfaces. The stomatal index was measured as 17.94 on the adaxial surface and 16.64 on the abaxial surface. These findings provide the first comprehensive anatomical characterization of O. vanensis and contribute to the documentation of its structural features for future taxonomic research.Onosma vanensis is an endemic species from Türkiye, and this study presents a detailed investigation of its anatomical features based on specimens collected from a newly recorded population in Muş province. Root, stem, and leaf tissues were examined using light microscopy to characterize the anatomical structure of the species. The roots display a well-developed secondary structure, in which the pith is entirely composed of tracheary elements and extensive xylem occupies a major portion of the cross-section. The stem has a uniseriate epidermis covered with setose and glandular trichomes, a 7–8 layered cortex, and a distinct vascular system with a 2–3 layered cambium. Leaves are isobilateral and amphistomatic, consisting of a uniseriate epidermis on both surfaces covered by a thin cuticle. The mesophyll thickness ranges between 234.5–328.8 µm, comprising 2(–3) layers of palisade parenchyma beneath the upper epidermis, a single palisade layer above the lower epidermis, and 3–4 layers of spongy parenchyma. Stomata are anomocytic to anisocytic, located at the same level as epidermal cells, and present on both leaf surfaces. The stomatal index was measured as 17.94 on the adaxial surface and 16.64 on the abaxial surface. These findings provide the first comprehensive anatomical characterization of O. vanensis and contribute to the documentation of its structural features for future taxonomic research.