Hesperomannia arborescens

No Common Name

Description

Hesperomannia arborescens is a small shrubby tree of the aster family that usually stands 5-16 ft (1.5-4.9 m) tall. Its typically hairless leaves, 4-8 in (10.2-20.3 cm) long and 1-3 in (2.5-7.6 cm) wide, range from oval to lance-shaped and are about two to four times as long as they are wide. The flower heads, which are about 2.4 in (6.1 cm) long, are either erect or ascending and grow singly or in clusters of two to ten. The flowers grow on thick, fuzzy stalks 0.2-0.6 in (5.1-15.2 mm) long and about 0.1 in (2.5 mm) in diameter. The involucre that surrounds each flower head is 0.8-1.4 in (2-3.6 cm) high, with the longest individual bracts growing to 1.1 in (2.8 cm). The yellow to yellowish-brown florets that comprise each head are about 0.9-1.2 in (2.3-3 cm) long and develop into 0.5-in-long (1.3-cm-long) achenes (dry, one-fruited fruits) topped with yellowish-brown or purple-tinged bristles. This member of an endemic Hawaiian genus differs from other Hesperomannia species in having erect to ascending flower heads, thick flower stalks, and usually hairless and relatively narrow leaves.

Habitat

H. arborescens typically grows on slopes or ridges in lowland wet forests and occasionally in scrub vegetation at elevations of 1,200-2,500 ft (365.8-762 m). Associated vegetation includes 'ohi'a, olopua, uluhe, hame, kopiko, and common Melicope species. The Molokai population grows in lama or 'ohi'a-dominated lowland mesic forests with the same elevation.

Distribution

H. arborescens was formerly known from locations on three islands: Kaiholena and Kukui on Lanai; Pelekunu Trail on Molokai; and scattered populations throughout the Koolau Mountains of Oahu, from Koolauloa and Pupukea at its northern extreme to Konahuanui at the southern end. This species is currently known from 15 populations on the islands of Oahu, Molokai, and Maui that totaled fewer than 100 individuals in 1997. Thirteen populations on Oahu have been observed since 1970 on private, state, and federal lands at a few disjunct locations over a distance of about 27 mi (43.5 km) in the Koolau Mountains; in 1997 Oahu had about 80 of these plants. Populations are located at Poamoho summit and stream, Waimanalo-Nui Divide, North Halawa-South Halawa Ridge, a ridge between Ohia ai-Oio gulches, Laie-Waimea Ridge, North and South Kaukonahua drainages, Maakua-Kaipapau Divide, Kapakahi Gulch, Lanipo summit, Opaeula stream, and Schofield Waikane.

On Molokai, one population of three individuals was found on state land in Olokui Natural Area Reserve. The range of H. arborescens was extended to Maui in 1989, when Joel Lau of the Nature Conservancy of Hawaii discovered two colonies of a single population 0.33 mi (0.5 km) apart on state land in West Maui National Area Reserve between Lanilili and Keahikauo.

Threats

The major threats to H. arborescens are 1) habitat degradation by feral pigs and goats; 2) competition with alien plants, especially Hilo grass, Koster's curse, and strawberry guava; 3) fire; 4) impact by humans; 5) stochastic extinction; and 6) reduced reproductive vigor due to its own limited numbers and weakened gene pool.

The single population on Maui is in an area that is subject to heavy pig damage, which is directly threatening the survival of these plants.

Conservation and Recovery

Attempted propagation of H. arborescens by state personnel has been unsuccessful, but the National Tropical Botanical Garden and the Lyon Arboretum have met with some success. The state has periodically removed weeds at the Laie population and the Maui Division of Forestry and Wildlife has fenced the four individuals in West Maui. Enclosures at all the other known populations need to be authorized.

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

Reference

U.S. Fish and Wildlife Service. 28 March 1994. "Endangered and Threatened Wildlife and Plants: Endangered Status for 11 Plant Species from the Koolau Mountain Range, Island of Oahu, HI." Federal Register 59 (59): 14482-14492.