Labordia lorenciana is described and illustrated from Kaua'i, Hawai'i, U.S.A. This new species most closely resembles the O'ahu endemic species Labordia kaalae C. N. Forbes, from which it differs in having leaf bases deeply cordate to auriculate, adaxial leaf surfaces puberulent, and fruit valves 25–37 mm long, and longitudinally striate. Known from only four individuals, Labordia lorenciana is amongst ca. 120 other rare Hawaiian taxa that are limited to less than 50 individuals and is currently being cultivated for conservation.