1 INTRODUCTION

Oceanic island systems are generally characterized by high endemicity due to their isolation, but at the same time the unique biodiversity of many islands is currently experiencing high extinction rates, primarily due to habitat reduction and pressure from invasive weeds and predators (Barnosky et al., 2011; Bruegman, Caraway, & Maunder, 2002). With 90% of its nearly 1,400 native plants classified as endemic, Hawai'i has one of the highest levels of endemism of any floristic region of the world (Wagner, Herbst, & Lorence, 2005; Wagner, Herbst, & Sohmer, 1999).

In 1991, a team of botanists from Hawai'i's National Tropical Botanical Garden helicoptered into the headwaters of a remote towering waterfall more than 500 m above sea level in Limahuli valley on northern Kaua'i (Figure 1a,b). During their botanical exploration one of the botanists, Ken Wood, made an extraordinary discovery: 12 plants of a new species of Cyanea with unusually narrow linear leaves (Wichman, 1992) (Figure 1c–e).

Figure 1 Open in figure viewer PowerPoint Cyanea kuhihewa Lammers. (a) Habitat North shore Kaua'i. (b) Map of Kaua'i showing Limahuli Valley. (c–e) Habit and flowers. Photographs and map (a,b) by Ken Wood; (c‐e) by David Lorence

Cyanea Gaudich. (Campanulaceae) is a genus comprised of branched and unbranched shrubs or palm‐like trees, which are endemic to Hawai'i. Seventy‐nine of the 85 known taxa are single island endemics. Cyanea species occur in mesic and wet‐forest habitat and are known for their colorfully arching flowers, and for their mutualistic relationship with several genera of nectarivorous Hawaiian honeycreepers (Fringillidae, Passeriformes) that provide pollination and dispersal of the fleshy fruits (Givnish et al., 2009; Lammers & Freeman, 1986).

Although Cyanea is one of the most species‐rich flowering plant genera in Hawai'i, nearly half of the known species are considered Endangered or Critically Endangered by the International Union for Conservation of Nature (IUCN) red list of threatened species and about 22 taxa are considered extinct in the wild (Wood, Oppenheimer, & Keir, 2019).

Only one Cyanea species with very narrow linear leaves was known at the time of the new Cyanea population discovery, namely Cyanea linearifolia Rock. That species was known only from the holotype collected on Kaua'i, along with a few additional specimens (Lammers, 1996), and was seen last in 1957. Consequently, C. linearifolia was presumed extinct probably due to the impacts of alien invasive species (Clark, 2016) and it was enthusiastically concluded that the 1991 collection represented a rediscovery of an extant population of a species presumed extinct (Wichman, 1992).

However, on subsequent comparison of Wood's specimen of the newly discovered population, with the type and other specimens of Cyanea linearifolia, Thomas Lammers (1996) concluded that the new finding was actually a discovery of a new species of Cyanea. Wood´s collection differed from C. linearifolia in having flat or slightly revolute leaf margins, fewer‐flowered pubescent inflorescences with shorter peduncles and bracts that were longer than wide, and larger pubescent flowers (Lammers, 1996) (Figure 1c–e). The new species was named Cyanea kuhihewa Lammers—kuhihewa meaning “to suppose wrongly” in Hawaiian language—a reference to the confusion with C. linearifolia (Lammers, 1996). Based on its extremely small population size and habitat, C. kuhihewa was assessed and considered Critically Endangered by the IUCN red list of threatened species (Lorence, 2016).

In 1992, shortly after the discovery of C. kuhihewa, the devastating hurricane Iniki severely impacted all of Kaua'i and destroyed portions of the forest canopy around Limahuli. The storm was followed by an influx of alien invasive plants and animals, including rats, slugs, and plant diseases, and the single population of C. kuhihewa declined until the last known individual died in 2003 (Lorence, 2016; Wood, 2007).

In 2017, another team of botanists from The Nature Conservancy of Hawai'i and the National Tropical Botanic Garden, discovered a hitherto unknown population of three C. kuhihewa individuals in a nearby valley, uncovering a new opportunity to protect and re‐establish this unique Kaua'i species. As of September 2019, this new population includes two mature and two juvenile C. kuhihewa, along with around 11 tiny seedlings (Wood, unpublished). Kamehameha Schools, The Nature Conservancy and the National Tropical Botanical Garden are working together to monitor and protect C. kuhihewa with multi‐annual visits to the area. Goodnature rat traps have been set up in the area to minimize the possibility of rat predation. More than 1,000 seeds have been collected since 2017 which are stored in seed banks or are under propagation at Lyon Arboretum (O'ahu island, Hawai'i) and the National Tropical Botanical Garden. As the propagated plants mature they will be out‐planted in the Upper Limahuli Preserve in the Limahuli valley on the north coast of Kaua'i, which is managed by the National Tropical Botanical Garden. Continued surveys are also being conducted in the hope of discovering additional unknown populations.