Aupaka (Isodendrion longifolium)
|Listed||October 10, 1996|
|Description||Slender, straight shrub; leaves are hairless and somewhat leathery; flower petals are purple.|
|Habitat||On steep slopes, gulches, and streambanks in mixed mesic or wet 'o'hia forest.|
|Threats||Habitat degradation and destruction by feral goats and pigs; competition with various alien plants; potentially threatened by overcollection and fire.|
Isodendrion longifolium is a slender, straight shrub of the violet family that generally grows between 2 and 7 ft (61 and 213 cm) in height. The hairless, somewhat leathery leaves are lance-shaped, 4-12 in (10.2-30.5 cm) long, and 1-3 in (2.5-7.6 cm) wide. The fragrant flowers are perfect and are borne singly along the branches. The five petals are purple, clawed, and somewhat unequal. The purple capsular fruit is 0.4 in (1.0 cm) long. This species is distinguished from others in this endemic Hawaiian genus by the shape of its leaves.
I. longifolium was first collected in 1840 in the Waianae Mountains of Oahu by members of the U.S. Exploring Expedition. Asa Gray later named this species for its long leaves. I. christensenii and I. maculatum are considered synonymous with I. longifolium.
I. longifolium is found at elevations between 1,350 and 2,500 ft (411 and 762 m) on steep slopes, gulches, and stream banks in mixed mesic or wet 'o'hia forest. Associated plant species include 'ahakea, hame, Cyanea sp. (haha), Hedyotis sp., Perrottetia sand-wicensis (olomea), and Pittosporum sp. (ho'awa).
I. longifolium was known historically from scattered locations on Kauai and in the Waianae Mountains on Oahu. I. longifolium is currently known from 19 populations on these two islands. In 1997, statewide populations of this species totaled fewer than 1,000 individuals.
Sixteen extant populations are scattered over ridges and valley slopes of northwestern Kauai including 500-800 total individuals noted on the island in 1997. Several hundred plants occurred in Limahuli Valley, about 100 on Mount Kahili, three east of Haupu Peak, an unknown number in the Iliiliula drainage, one in the Wainiha-Manoa drainage, 25 near Wainonoia Stream, and several hundred in the Wahiawa Mountains on private land. One individual occurred on Hanakapiai-Hoolulu Ridge, 15-20 in Hanakapiai, at least nine in Kawaiula Valley, 10 in Kalalau Valley, 80-90 in Waioli Valley, and approximately 20 in Limahuli on state land, which includes Hono O Na Pali Natural Area Reserve and the Na Pali Coast State Park.
Three populations of fewer than 30-40 total individuals were known on Oahu in 1997. Two populations, one in Palikea Gulch of an unknown number of individuals and one of 25-30 individuals in Kaawa Gulch, were found within Mt. Kaala Natural Area Reserve on state-owned land in the Waianae Mountains. An unconfirmed specimen was collected in Makaua Gulch in the Koolau Mountains on private or state land.
The larger distribution of populations and total numbers of plants reduce the likelihood that this species will become extinct in the near future. However, I. longifolium is likely to become endangered in the foreseeable future if the threats affecting it are not reduced.
The major threats to I. longifolium are habitat degradation and destruction by feral goats and pigs and competition with various alien plants. On Oahu, the Palikea Gulch population is potentially threatened by overcollection and fire.
Two populations of I. longifolium on Kauai have sustained loss of individual plants and habitat as a result of feral pig activities. One population of I. longifolium on Oahu is threatened by pigs, and goats are contributing to the decline of one population of this species on Kauai.
I. longifolium, whose populations are well-known and close to trails, is threatened by trampling and overcollection.
Cattle, deer, and goat predation is a possible threat for this plant since it is not known to be unpalatable to these animals.
Lantana poses a threat to one population and strawberry guava directly threatens four populations of I. longifolium on Kauai, as well as one population on Ohau. Thimbleberry poses a threat to five populations on Kauai, while Koster's curse threatens two populations in Waioli Valley on Kauai. In the Waianae Mountains of Oahu, Koster's curse poses a serious threat to one population; on Kauai, Hilo grass threatens the Wahiawa Mountains and Waioli Valley populations. Common guava poses a threat on Kauai to a population in the Waioli Valley.
Fire poses a potential threat to populations of I. longifolium. Accidentally or maliciously set fires in residential areas near the Lualualei Naval Magazine and the Makua Military Reservation on Oahu could easily spread and pose a possible threat to a nearby population of I. longifolium.
Conservation and Recovery
I. longifolium has been successfully propagated at Lyon Arboretum's micropropagation laboratory, but outplanting has not been attempted.
Coordinated fire protection is needed for endangered plant species on state natural area reserves, such as Mt. Kaala, where one of three Oahu populations of I. longifolium occurs.
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
U. S. Fish and Wildlife Service. 10 October 1996. "Determination of Endangered or Threatened Status for Fourteen Plant Taxa From the Hawaiian Islands." Federal Register 61 (198): 53108-53124.