Na'ena'e (Dubautia latifolia)
|Listed||May 13, 1992|
|Description||Woody vine with opposite, untoothed leaves and clusters of yellow flower heads.|
|Habitat||Well-drained slopes in moist mountain forests.|
|Threats||Invasive alien plant species, low reproduction.|
Dubautia latifolia (Na'ena'e) is a branched, woody vine of the aster family that grows to a height of 26 ft (7.8 m). The opposite, elliptical to oblong-elliptical leaves are 3 to 6.6 in (7.5 to 16.5 cm) long and 1 to 3 in (2.5 to 7.5 cm) wide. They have distinct leaf stems (petioles), untoothed margins, and are conspicuously net-veined. Small, yellow flower heads occur in dense clusters at the ends of the branches; the fruits are small dry seeds. Dubautia latifolia is distinguished from similar species in this endemic genus by its vining growth habit, and the distinct petioles and net-veins of the leaves. Dubautia latifolia has also been known by the names Railliardia latifolia and Railliardia latifolia var. helleri.
Dubautia latifolia is one of a large number of species endemic to the Kokee area in the northwestern part of the Kauai, an area roughly encompassed by the 8 sq mi (20.8 sq km) of Kokee State Park. Kokee State Park lies just north of Waimea Canyon, and has the Alakai Swamp to the east, the steep cliffs of the Na Pali coast to the north, and drier leeward ridges to the west. Dubautia latifolia is found on well-drained, semi-open slopes in the moist Acacia koa forests of Kokee at elevations between 3,200-3,900 ft (960-1,170 m). Dubautia latifolia also grows in a more limited way in closed Metrosideros polymorpha forests and in conifer plantations.
Five other plant species endemic to the Kokee region are federally listed as Endangered: Chamaesyce halemanui, Hawaiian bluegrass (Poa sandvicensis ), Poa siphonoglossa, Stenogyne campanulata, and Xylosma crenatum.
Dubautia latifolia was first collected in 1840. Subsequently it has only been known from six areas of northwestern Kauai: Mukaha and Awaawapuhi valleys in Na Pali-Kona Forest Reserve, Nualolo Trail and valley in Kuia Natural Area Reserve, Halemanu in Kokee State Park, along Mohihi Road in Kokee State Park and Na Pali-Kona Forest Reserve, along the Mohihi-Waialae Trail on Mohihi and Kohua ridges in Na Pali-Kona Forest Reserve and Alakai Wilderness Preserve, and Kaholuamanu on privately owned land.
Dubautia latifolia survives presently at all historic sites except Halemanu in Kokee State Park and the privately owned Kaholuamanu. Each of the surviving populations is on state land, covers an area of from 25-1,600 sq ft (2.25-144 sq m) and consists of less than six individual plants. The total population of Dubautia latifolia is believed to be about 100 plants.
Dubautia latifolia appears to be self-incompatible. Since at least some individuals require cross-pollination, the wide spacing of individual plants, about 0.3 mi (480 m) apart, may pose a threat to the reproductive potential of the species. The very low seed set noted in plants in the wild indicates a reproductive problem, possibly flowering asynchrony. Seedling establishment is also rare and young plants are rarely seen. Dubautia latifolia experiences seasonal vegetative decline during the spring and summer, often losing most of its leaves. New growth and flowering occur in the fall with fruits developing in November. Pollinators and seed dispersal agents are unknown.
The main threat to the survival of Dubautia latifolia is competition from alien plant species, most notably banana poka, which is invading the habitat of almost all known populations. Banana poka, an aggressive vine with an ecological niche similar to that of D. latifolia, kills trees by completely covering their canopies with heavy vines. The resulting forest openings promote the growth of other alien plant species at the expense of native plants. Blackberry, strawberry guava, black wattle, Australian blackwood, ginger, and Japanese honeysuckle threaten to displace Dubautia latifolia and other endemic native species.
In the Kuia Natural Area Reserve, illegal marijuana cultivation is a threat to native species, including Dubautia latifolia. Not only is native flora destroyed in clearing land for cultivation, but alien species are introduced into the area from material brought to the site.
Conservation and Recovery
The U.S. Fish and Wildlife Service published a Recovery Plan for the Dubautia latifolia and co-occurring endangered species in 1995. All of its known populations are on state-owned land, and its habitat is being managed to keep it in a relatively natural condition. However, the Dubautia latifolia remains threatened by introduced plants and mammals. Its habitats should be managed to reduce or eliminate these non-native pests. The population of the Dubautia latifolia should be monitored, and research undertaken into its biology and habitat needs. The Dubautia latifolia has been successfully propagated at National Tropical Botanical Garden, and this garden has seeds of the endangered plant in storage.
U.S. Fish and Wildlife Service
Oregon Fish and Wildlife Office
2600 Southeast 98th Avenue, Suite 100
Portland, Oregon 97266-1398
Telephone: (503) 231-6179
Fax: (503) 231-6195
U.S. Fish and Wildlife Service
Senior Resident Agent-Honolulu, Hawaii
P.O. Box 50223
300 Ala Moana Boulevard, Room 7-235
Honolulu, Hawaii 96850-5000
U.S. Fish and Wildlife Service. 1995. "Recovery Plan for the Kauai Plant Cluster." U.S. Fish and Wildlife Service, Portland, Oregon.