Hesperomannia arbuscula

No Common Name

Description

Hesperomannia arbuscula is a shrub or small tree in the aster family that grows to 11 ft (3.4 m) in height. The leaves are alternate, elliptic, and from 4-7 in (10.2-17.8 cm) long. The erect flower heads occur in clusters of four or five. Each head is comprised of numerous yellow or yellowish-brown florets. This species usually flowers in the spring, depending on precipitation. Seeds mature in about six weeks, and the trees live 10-15 years.

The species has also been known by the names H. arborescens var. oahuensis, H. arbuscula ssp. oahuensis, H. arbuscula var. pearsallii, H. mauiensis, and H. oahuensis.

Habitat

H. arbuscula grows on slopes and ridges in moist to wet forests at elevations of 1,200-3,000 ft (365.8-914.4 m) throughout the Waianae Mountains. These forests are dominated by koa (Acacia koa ) and 'ohi'a (Metrosideros polymorpha ). Associated species include ko'oko'olau (Bidens ), maile (Alyxia oliviformis ), and kopiko (Psychotria ).

Distribution

H. arbuscula had historical occurrences from Makaleha to Puu Kanehoa in the central and southern Waianae Mountains of Oahu, as well as from West Maui. This species is now extant on Oahu in four populations within an area of about 2 by 5 mi (3.2 by 8 km) on state and private land at the Makaha-Waianae Kai Ridge, in Kaluaa Gulch, and in Kapuna Gulch. Two populations occur at the first location, and these had respective numbers in 1997 of 50 and 20 plants. The second location had five to seven plants, and the third location had 13 plants. In addition to the approximately 90 individuals on Oahu in 1997, there was one plant growing in the Iao Valley of West Maui.

Threats

As for most rare Hawaiian plants, the main threats to H. arbuscula are habitat degradation by feral pigs and competition from alien plant species.

The extremely low number of known plants and their limited distribution makes the species vulnerable to extinction through unpredictable natural or human-precipitated events. The proximity of some populations to trails exposes plants to an increased danger of collection or trampling by hikers.

Conservation and Recovery

The Division of Forestry and Wildlife has weeded the Pahole National Area Reserve population and removed Koster's curse and Christmasberry. They also have plans to outplant H. arbuscula at one of the Pahole National Area Reserve outplanting enclosures. This species is being propagated at the National Tropical Botanical Garden and the Lyon Arboretum.

Contacts

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

Pacific Remote Islands Ecological Services Field
Office
300 Ala Moana Blvd., Room 3-122
P. O. Box 50088
Honolulu, Hawaii 96850
Telephone: (808) 541-1201
Fax: (808) 541-1216

References

Cuddihy, L. W., and C. P. Stone. 1990. Alteration of Native Hawaiian Vegetation: Effects of Humans, Their Activities, and Introductions. Cooperative National Park Resources Study Unit, University of Hawaii Press, Honolulu.

Stone, C. P., and J. M. Scott, eds. 1985. Hawaii's Terrestrial Ecosystems: Preservation and Management. Cooperative National Park Resources Study Unit, University of Hawaii Press, Honolulu.