Here we report a previously unrecorded species of Korean Myriophyllum L. (Haloragaceae). This taxon, M. oguraense Miki has been regarded as a Japanese endemic for some 60 years. Myriophyllum oguraense and its closely related M. verticillatum L. share the characteristic of having pectinate emergent leaves that are similar in shape to, but much smaller than, the submerged leaves. However, the primary characteristic that differentiates these taxa is the turion shape (club shaped in M. verticillatum and linear in M. oguraense). The common name, ‘Gin-dong-a-mul-su-sae-mi’ was also newly given considering its characteristic turion shape. Photographs and a key to Korean Myriophyllum species are provided in addition to complete descriptions including information on nomenclatural types, distributions and specimens examined.