The Oahu sedge (Carex oahuensis var. robusta) belongs to Cyperaceae (the Sedge family). It is a perennial evergreen herb that is distrbuted westward from Kanto district of Honshu to Shikoku, Kyushu of Japan, Taiwan and the Korean Peninsula. This herb grows on the coastal rocks and sands, and can reach 30-40 cm in height. The stems are clumping and form large clumps. The leaves are linear 5-10 mm in width, stiff and glossy. The 3-6 spikelets are borne on the uuper stems from April to June. The acrogyrous spikes are male and the pleurogerous spikes are female.