An Unrecorded Variety of Ceratophyllum (Ceratophyllaceae) in Korea: Ceratophyllum demersum var. inerme J. Gay ex Radcliffe-Sm

We report an unrecorded variety, Ceratophyllum demersum var. inerme from Jeju-do, South Korea. This taxon is similar to C. demersum var. demersum by 1-2 × dichotomously divided leaves, but it is easily distinguished from the other varieties of C. demersum by absent of basal spines on the fruit. We provide accurate a description, photographs, and guidelines to distinguish this variety from other related taxa in Korea. Our findings will not only contribute to increasing biodiversity of South Korea, but will also be used as important basic data to conserve the taxon, which shows a limited distribution within the Korean Peninsula.