An unrecorded alien species plant, Phalaris paradoxa L. (Poaceae) was found in Andeok-myeon, Seogwipo-si, Jeju island, Korea. It is native to the Mediterranean region of Europe, and it is currently found worldwide. Phalaris paradoxa is distinguishable from related taxa (P. arundinacea, P. canariensis, P. minor and P. arundinacea var. picta) in Korea by the following combination of characterstics: spikelets in clusters (the upper central fertile spikelet surrounded by six lower sterile spikelets), wing of the keel. This taxon was named ‘Nal-gae-ca-na-ri-sae-pul’ in Korean based on its character. We provide its description, illustrations, photographs and a key of related taxa in Korea.