The genus Juncus L., comprising approximately 310 species, is a perennial herbaceous plant with the highest species diversity among Juncaceae. Although external leaf morphological and anatomical characteristics were used for taxonomic delimitation of Korean Juncus taxa, the micromorphological structure of Juncus is not comprehensively described. Our main objective was to determine whether leaf micromorphological comparisons among the studied Korean Juncus taxa could provide taxonomically informative characteristics. Korean rushes possessed both unifacial and bifacial leaves, although the patterns of cell outlines on the abaxial surfaces of cataphyll and cauline leaves and stems were similar. Leaf and stem epidermal cells were irregularly arranged and exhibited rectangular, rhomboidal, and polygonal shapes. Striations on epidermal cells are common in almost all species of the genus Juncus; however, scaly epicuticular wax is found only in J. setchuensis. The stomatal complexes of the studied Korean Juncus taxa were uniformly paracytic (stomata surrounded by two subsidiary cells), regardless of their occurrence in cataphyll and cauline leaves or on the stem surface. Guard cell length could be important taxonomic characters in Korean Juncus taxa, in accordance with traditional taxonomy, which distinguishes the two subgenera based on morphological characters. Differences in guard cell length and stomatal density were also influenced by external environmental factors but were not clearly correlated with variations in ploidy levels.
