Taxonomic Identification of Ligustrum foliosum Nakai: A Comprehensive Study of Macro- and Micromorphology

Ligustrum foliosum Nakai, a species endemic to South Korea, is a member of the Oleaceae family. This study provides a comprehensive taxonomic identification of L. foliosum based on its macro- and micromorphological characteristics, particularly focusing on the leaf foliar epidermal taxonomy. Scanning electron microscopy (SEM) was used to analyze the leaf structures of L. foliosum collected from various populations on Ulleungdo Island, its primary habitat. Macromorphological assessment revealed that L. foliosum exhibits ovate to elliptical leaves with pointed apices, rounded bases, and entire, smooth margins. The leaves measured 3–10 cm in length and 1.5–4 cm in width, with a pinnate venation pattern and prominent secondary veins. The adaxial surface was dark green and glabrous, while the adaxial surface was lighter green and slightly pubescent. Micromorphological analysis using SEM provided detailed insights into the leaf epidermal characteristics. The epidermal cells were polygonal in shape with straight to slightly curved anticlinal walls. Anomocytic stomata that were not surrounded by specialized cells are the predominant type, with a density ranging from 100 to 150/mm². Epidermal cells measured approximately 10–20 μm in length and 5–10 μm in width, while the stomata typically measured approximately 20–30 μm in length and 10–15 μm in width. Thick-walled bundle sheath cells were evident around the vascular bundles, with a density of 1–3 bundles/mm. The cuticle was moderately thick, providing protection against desiccation, and trichomes were elongated single cell on the leaf both surface. This study contributes to the understanding of L. foliosum's taxonomic position within the Oleaceae family by providing a detailed description of its macro- and micromorphological characteristics. These findings can aid in the identification and conservation of this endemic species, which is crucial for preserving the unique biodiversity of Ulleungdo Island and South Korea.