Two unrecorded species of Najas L. (Hydrocharitaceae) from Korean flora: N. orientalis and N. oguraensis

We report Najas orientalis Triest & P. Uotila and N. oguraensis Miki as unrecorded species from the Korean flora. N. orientalis is distinct from other Najas species in having rounded leaf sheaths and raised testa in the cell walls, and in that this species occurs in the southern region of Korea (Gimhae, Gangjin). N. oguraensis is close to N. minor, but is distinct from this species by having larger male flowers and 4-celled anthers. This species is distributed in the southern region of Korea (Changwon, Jangheung). We also give a new Korean common name for N. gracillima (A. Braun ex Engelm.) Magnus, which is widely distributed in South Korea. A taxonomic key to the six species of Najas is given.