Dwarf Naupaka

Scaevola coriacea

Description

The Scaevola coriacea (dwarf naupaka) is a sparsely branched, prostrate shrub. Its older stems are somewhat woody, and the leaves are relatively far apart, giving the plant a sparse appearance. Its succulent leaves are thick, light green, and about 1 in (2.5 cm) in length. Its cream-colored flowers may open at any time during the year. Typical of this genus, the flower resembles half of a symmetrical flower that has been divided long-wise, sometimes referred to as a "half flower." The fruit is purplish black and contains two seeds. The S. coriacea is distinguished from other species of Scaevola by its prostrate habit and thick, succulent leaves. A strong colonizer, an individual dwarf naupaka may spread over an area of 108 sq ft (10 sq m).

Habitat

The dwarf naupaka grows in low, firmly packed, coastal sand dunes, where most plants grow at or near ground level. The habitat is relatively dry, hot, and isolated from other vegetational zones. Associated species include S. taccada (a common, shrubby member of the same genus), Bidens mauiensis, Nama sandwicensis, Boerhavia diffusa, and Lipochaeta integrifolia.

Distribution

The dwarf naupaka was once distributed throughout the major Hawaiian islands. It was historically recorded on the islands of Hawaii, Kauai, Lanai, Niihau, and Oahu, but is now extirpated there. It survives on Maui and on two offshore islets off West Maui and Molokai.

Threats

The primary threats responsible for the drastic decline of the dwarf naupaka include browsing by cattle, the loss of habitat due to building and road construction, and other impacts of human activities. More recently, it has been threatened by the development of coastal areas for housing and commercial developments. On the central isthmus of Maui and northeast West Maui, coastal dunes have been almost completely replaced by development.

In 1986, only four populations of dwarf naupaka, totaling 350 individual plants, remained at Waiehu Point (West Maui), Kaupo (East Maui), Mokeehia (an islet off West Maui), and Mokuhooniki (an islet east of Molokai). The Waiehu Point population grows on sand dunes, which extend over part of the state-owned Waiehu Golf Course and onto a tract of private land that is being developed into a residential subdivision. Development of this site will reduce the total amount of available habitat by nearly two-thirds. The Kaupo population is entirely on private land. Mokuhooniki is part of the Hawaiian State Seabird Sanctuary, and access to the islet is strictly controlled, requiring a state permit.

The continuing loss of habitat to residential development is the most immediate threat to the dwarf naupaka. Ultimately, the only way to save this rare shrub is to preserve its remaining beachfront habitat. This will require a cooperative effort by federal, state, and county agencies and private landowners. In addition, at all four of its known sites, the dwarf naupaka is being crowded out by aggressive non-native plants, such as Leucaena leucocephala, Ficus microcarpa, and Wedelia trilobata. The dwarf naupaka is also being affected by trampling and erosion in the vicinity of golf courses. The Kaupo population is somewhat threatened by feeding and trampling by cattle. Though unfenced, the plants are protected from more substantive damage by the steep slope on which they grow at this site. In addition, because it is an attractive plant and sites are easily accessible, the dwarf naupaka has been collected for planting in private gardens.

Conservation and Recovery

The recovery plan for the dwarf naupaka recommends establishing Make'ehia and Mokuho'oniki Islets as managed sanctuaries. The plan also recommends establishing the dunes within the golf course at Waiehu as a state sanctuary.

The dwarf naupaka is easily propagated in captivity and has potential for cultivation and sale as an ornamental. The Recovery Plan recommends maintaining genetic diversity through carefully managed propagation. In addition, seeds should be stored in a seed bank for future propagation.

Because the dwarf naupaka cannot compete well with weeds, the control of aggressive plants within its habitat is important.

Contacts

U.S. Fish and Wildlife Service
Pacific Islands Ecoregion
300 Ala Moana Boulevard, Room 3-122
Box 50088, Honolulu, Hawaii, 96850
Telephone: (808) 541-3441
Fax: (808) 541-3470

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Eastside Federal Building
911 N. E. 11th Ave.
Portland, Oregon 97232-4181
Telephone: (503) 231-6121
http://pacific.fws.gov/

References

Carr, G. D. 1981. "Unpublished Status Survey of Scaevola coriacea." U.S. Fish and Wildlife Service, Honolulu.

Herbst, D. R. 1972. "Botanical Survey of the Waiehu Sand Dunes." Bulletin of the Pacific Tropical Botanical Garden 2:6-7.

U.S. Fish and Wildlife Service. 1986. "Determination of Endangered Status for Scaevole coriacea (Dwarf Naupaka). Federal Register 51 (95): 17971-17974.