Lysimachia barcae (Primulaceae), a new endemic shrub from Wainiha, Kaua‘i, Hawaiian Islands

A new endemic species of <i>Lysimachia</i> from Kaua'i, Hawaiian Islands, is described and illustrated with notes on its distribution, ecology, conservation status and phylogenetic relationships. A modification to the existing key for Hawaiian <i>Lysimachia</i> is provided. <i>Lysimachia barcae</i> <b>sp. nov.</b>, differs from its Hawaiian congeners by its unique combination of mature stems villous to tomentose, petioles 1-3 mm long, leaves ovate, cordate to subcordate or rounded at base, with primary and secondary veins conspicuous, purple-red, raised on abaxial surface, often densely hirsute to pilose and pedicels 35-70 mm long. Only ten mature individuals are known from a single colony along steep, precipitous slopes of Wainiha Valley, Kaua'i. <i>Lysimachia barcae</i> represents a new Critically Endangered (CR) single-island endemic species and is the focus of concerted conservation efforts to prevent its extinction.