Abstract
A new endemic species of Geniostoma from Kaua'i, Hawaiian Islands, is described and illustrated with notes on its distribution, ecology, conservation status, and relationships to other members of the genus. A modification to the existing key for Hawaiian Geniostoma is provided along with a key to all Kaua'i species. Geniostomaimadae sp. nov., differs from its Hawaiian congeners by its unique combination of glabrous stems, leaves and stipules, flowers 3-10 in open, paniculate cymes with peduncles up to 75 mm long, corolla salverform, lobes 9-11 mm long, calyx lobes 5-9 mm long, and capsules 2-valved with beak 2-4 mm long. Population estimates range from 800 to 1250 individuals distributed across the central northern and eastern windward ridges, slopes and valleys of Kaua'i. Geniostomaimadae represents a new Vulnerable (VU) single-island endemic species.