Taxonomic Significance of Leaf Anatomy of the Genera Canthium Lam., Canthiumera K.M.Wong & Mahyuni, Meyna Roxb. ex Link, and Psydrax Gaertn. (Rubiaceae: Vanguerieae) in Thailand

The taxonomic significance of leaf anatomy within the genera Canthium, Canthiumera, Meyna, and Psydrax (Rubiaceae: Vanguerieae) in Thailand were investigated. Leaf and petiole anatomy of eight species of Canthium, one species of Canthiumera K.M.Wong & Mahyuni, three species of Meyna Roxb. ex Link, and three species of Psydrax Gaertn. were analyzed using the transverse sections, epidermal peels, and scanning electron microscopy (SEM). Anatomical characters were evaluated using Principal Component Analysis (PCA) and Unweighted Pair Group Method Algorithm (UPGMA). The anatomical analysis indicates that the genera can be distinguished based on the number of palisade mesophyll layers, the presence or absence of stomata on the leaf surface, and the presence or absence of an adaxial parenchymatous hypodermis. Anatomical features support the recognition of Canthium in a narrow sense: Canthium, Canthiumera, Meyna, and Psydrax. These findings emphasize the potential of leaf anatomical characters as a reliable tool for taxonomic classification.