In 2003, the National Park Service acquired 46,943 ha of Kahuku Ranch, in the Ka'u district of Hawai`i. This addition to Hawai`i Volcanoes National Park includes a diverse assemblage of vegetation communities. Since little was known about the communities and their floristic composition, appropriate management practices could not be developed. Surveys conducted between 2004 and 2006 in Kahuku described vegetation communities and located rare, threatened and endangered plants, as well as disruptive alien weeds. Forty-one kilometers of transects and 177 vegetation plots were ground-surveyed, and 6.5 hours of helicopter surveys were conducted. Surveys encountered a total flora of 455 vascular plant species, of which 40% were native. Five endangered, one threatened, one candidate endangered, and seven species of concern were found, as well as 26 locally rare native species. Forty-three disruptive alien plant taxa in and near Kahuku were mapped. Several sites containing high numbers of either rare or invasive plants were identified.