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Cyanea kuhihewa: Rediscovering one of Hawai’i’s rarest trees

By Nina Rønsted and Kenneth R. Wood


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).

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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.

2 THE UNIQUE HAWAIIAN FLORA

Cyanea is one of six genera of Hawaiian lobeliads, which are a group of circa 126 species in the bellflower family, Campanulaceae, all of which are endemic to Hawai’i, and considered to be one of the most spectacular examples of adaptive radiation in plants (Givnish et al., 2009). The origin of this group has been debated because morphological data indicate multiple independent colonization events. However, based on molecular phylogenetic data, the Hawaiian lobeliads likely arrived at the Hawaiian islands by a single‐dispersal event about 13 million years ago (Givnish et al., 2009). Accelerated speciation and adaptive radiation in habitat, followed by changes in elevation and flower‐tube length in Cyanea, resulted in Hawaiian lobeliads being the most species‐rich single‐origin radiation of plants resolved on any single oceanic island or archipelago, making them a model case for understanding island speciation (Givnish et al., 2009; Lammers, 2007).

Oceanic island systems are generally characterized by high endemicity due to their isolation. With its wide range of bioclimatic zones, abundance of freshwater and sunlight critical to life, and lack of natural predators, Hawai’i developed into one of the major “hot spots” on Earth for plant endemism (Brooks et al., 2002; Steinbauer et al., 2016). With 90% of the 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 et al., 20051999). Just like the Cyanea, many of these species are uniquely adapted to, and dependent on, their natural habitats, and are critical components of the local ecosystem.

3 A HAWAIIAN EXTINCTION CRISIS

In addition to its distinction as a global hotspot of endemism, Hawai’i has also recently been presented as a global extinction capital (Humphreys, Govaerts, Ficinski, Nic Lughadha, & Vorontsova, 2019), with about 134 native Hawaiian plant species reported extinct since the 1840s (Bruegmann et al., 2002; Wood et al., 2019). In comparison to continental sites, these species have an exceptionally slim chance of ever being rediscovered (Humphreys et al., 2019). Nearly 240 Hawaiian plant species, 34 Cyanea species among them, are considered to have fewer than 50 individuals left in the wild, which is a criteria for a plant being considered Critically Endangered according to the IUCN red list of threatened species (IUCN, 2020; Plant Extinction Prevention Program, 2019) highlighting a more general ongoing extinction crisis in Hawai’i. There are several reasons for this endangerment, including habitat destruction, loss of pollinators and seed dispersers, invasive plants and animals, introduced diseases, and climate change (Barnosky et al., 2011; Bruegmann et al., 2002; Lammers & Freeman, 1986).

4 CONSERVING THE UNKNOWN

Hawai’i shares this pattern of decline and extinction with other island groups and many of these threatened species will not survive without extensive management, including habitat protection, restoration, and control of invasive weeds, animals and diseases (Bruegmann et al., 2002). In addition, carefully monitored ex situ conservation in seed banks and through propagation in living collections, as well as out‐planting, can contribute to conserve genetically healthy populations of these species (Fant et al., 2016). Governmental, non‐governmental organizations, and botanical gardens, must work together to address the extinction crisis. In Hawai’i, this is being implemented though the Hawai’i Conservation Alliance, which is a partnership of organizations and agencies working together to provide unified leadership, advocacy, and collaborative action to conserve and restore native ecosystems and the unique biodiversity of the islands of Hawai’i (Hawai’i Conservation Alliance, 2020). Successful conservation schemes are dependent on knowing and understanding the flora, however, several of the world’s most biodiverse countries and island systems are still lacking thorough floristic investigation, prohibiting formal assessment of threatened species, as well as meta‐analyses of changes in floristic patterns (Lack, 2012). When considering the extremely narrow endemicity and rarity of many island species, taxonomic confusion such as that surrounding C. kuhihewa, as alluded to by its name, may indeed be a serious impediment for assessing and improving the conservation status of a species.

5 CONCLUDING REMARKS

The flora of Hawai’i is a hotspot of endemism, but the uniquely adapted native flora is highly vulnerable to disturbance, and losing just a few populations may mean losing one or more species. C. kuhihewa is one of about 85 taxa in this genus of charismatic Hawaiian lobeliads, most of which are uniquely adapted to a single island or are even narrower endemics from a single mountain or valley. About half of the genus is considered threatened, most of them with fewer than 50 individuals remaining in the wild. Reports of rediscovery of species previously thought to be extinct are always encouraging news, and we may still be able to safeguard C. kuhihewa through the ongoing combination of monitoring, weed and predator control, seed‐banking, propagation, and out‐planting.

ACKNOWLEDGEMENTS

Kamehameha schools and The Nature Conservancy of Hawai’i supported the fieldwork that led to the rediscovery of C. kuhihewa in 2017. Fondation Franklinia is thanked for financial support for the conservation of C. kuhihewa under the project Endangered Endemic Trees of Kaua’i project number 2020‐4.

Originally published by The New Phylogist Trusthttps://nph.onlinelibrary.wiley.com/doi/full/10.1002/ppp3.10099