Cyperus pacificus has been the subject of considerable taxonomic confusion since its introduction as a new taxon, based on specimens that were previously identified as C. michelianus. Descriptions of key diagnostic characters, such as the glume arrangement, vary across the literature, further complicating the segregation of these taxa. In this study, we aimed to resolve taxonomic issues related to these species by conducting a morphological comparison of Korean specimens of C. pacificus (var. pacificus and var. margoinflatus), Japanese specimens of C. pacificus (var. pacificus and var. margoinflatus), and Taiwanese specimens of C. michelianus. Our results indicate that most Korean specimens can be reidentified as C. michelianus, with some specimens being found to contain both C. michelianus and C. pygmaeus mounted together on the same sheet. C. michelianus is characterized by spirally arranged glumes on the dorsal, lateral, and ventral surfaces, slightly convex spikelets, and relatively long, flexible awns. In contrast, C. pacificus is distinguished by its flat spikelets and glumes that are typically arranged distichously, with either the base or only one side spirally arranged. Furthermore, C. pacificus taxa can be differentiated from C. michelianus by their generally shorter and straighter awns. The two taxa of C. pacificus studied here, var. pacificus and var. margoinflatus, are distinguished by the presence of a distinctly swollen wing at the achene margin of the latter taxon. This study is the first to clearly establish the presence of C. michelianus in Korea and provides detailed descriptions and diagnostic characters for related taxa. The findings also imply the need for targeted field surveys to clarify the distribution and status of C. pacificus in Korea.
KIM et al. (Sat,) studied this question.