Peperomia kauaiana (Piperaceae), a new alternate-leaved species from Kaua‘i, Hawaiian Islands and notes on two possibly extinct Hawaiian Peperomia

A new species of Peperomia with alternate leaves from Kaua‘i, Hawaiian Islands, is described and illustrated, with notes on its conservation status, distribution and ecology. We present a dichotomous key to all five Hawaiian Peperomia species with alternate leaves and include notes on two possibly extinct Hawaiian Peperomia species, namely P. degeneri and P. subpetiolata. Peperomia kauaiana sp. nov. differs morphologically from its Hawaiian congeners by its unique combination of diminutive leaves 5–14 (– 18) mm long, 4–11 (– 14) mm wide, palmately 5 - to 7 - nerved, ovate to ovate-orbicular with margins revolute, petioles 2–5 mm long and spikes 11–17 (– 22) mm long.

Plants have been documented in three distinct windward Kaua‘i locations to date, including the southern ridges of Wahiawa, the central ridges of Wai‘ahi and the north-eastern ridges of the Makaleha Mountains. Peperomia kauaiana represents a newly-described wet forest species endemic to the island of Kaua‘i and is currently in need of conservation. Its discovery raises the total number of endemic Hawaiian Peperomia species to 24 and single-island endemic Peperomia on Kaua‘i to three.