Sesbania tomentosa, commonly known as Oahu riverhemp and ʻōhai, is an endangered species of plant in the pea family, Fabaceae, that is endemic to the main Hawaiian Islands as well as Nīhoa and Necker Island. It inhabits low shrublands and, rarely, dry forests, at elevations from sea level to 2,500 ft (760 m). Associated native plant species include ʻakiʻaki, ʻilima, naupaka kahakai, and pili. Off-road vehicles, wildfires, grazing, and alien species competition have destroyed their habitat on the main islands, but they are still quite common on Nīhoa and Necker. At least 2,000 specimens grow on Nīhoa, while there are far less on Necker.