Aupaka

Isodendrion laurifolium

Description

Isodendrion laurifolium is a slender, straight, and few-branched shrub of the violet family (Violaceae) that generally reaches a height of 3-6 ft (91.4-182.9 cm). The leaves, 2-6 in (5.1-15.2 cm) long and 0.6-2.0 in (1.5-5.1 cm) wide, are somewhat leathery, oblong-elliptic, narrowly elliptic lance-shaped, or rarely elliptic. The fragrant flowers are perfect and borne singly along the stems. The five clawed and somewhat unequal petals are purple with greenish white external edges, while the inner face of the lobe is dusty purple. The fruit is a green, lance-shaped capsule. This species is distinguished from others in this endemic Hawaiian genus by the shape of its leaves.

I. laurifolium was first described by Asa Gray in 1852 from a collection made on Oahu by members of the U.S. Exploring Expedition in 1840. Other published names considered synonymous with I. laurifolium are I. forbesii, I. lydgatei, I. subsessilifolium, and I. waianaeense. The specific epithet refers to the resemblance of the leaves to those of the laurel tree.

Habitat

I. laurifolium is usually found from 1,620 to 2,700 ft (494 to 823 m) in elevation in diverse mesic forest, or rarely wet forest, dominated by o'hia' or koao'hia', or o'hia'-lama with hame, maua, Hedyotis terminalis (manono), Pisonia sp. (papala kepau), and Pouteria sp. ('a'ali'i).

Distribution

I. laurifolium had historical occurrences at scattered locations on Kauai and in both the Waianae and Koolau mountains of Oahu. The 14 extant populations on these two islands numbered between 190 and 210 individuals in 1996.

Approximately 130-140 individuals were known on Kauai from eight populations at the following locations: five plants occurred in Paaiki Valley, about 20 in Kawaiula Valley, more than 50 in Haeleele Valley, more than 40 in Makaha Valley, 10-20 in Poopooiki Valley, two each in Mahanaloa and Kuia Valleys, and one in the Koaie branch of Waimea Canyon. All Kauai populations are on state-owned land, with several in Kuia Natural Area Reserve.

Six populations of approximately 60-70 total individuals were noted on Oahu in 1996, including more than 40 plants that occurred on City and County of Honolulu land in Makaha in the Waianae Mountains. Additionally there were four in eastern Makaleha Valley, 10 or fewer in Waianae Kai, nine in Kaawa Gulch, and six on state land including Mt. Kaala Natural Area Reserve in Kaumokunui Gulch in the Waianae Mountains. Two plants also occurred in south Kaukonahua Gulch within the federally owned Schofield Barracks Military Reservation in the Koolau Mountains.

Threats

The primary threats to I. laurifolium are habitat degradation caused by black-tailed deer, goats, and pigs; competition with invasive alien plants; and potential harm from military activities.

One population of I. laurifolium on Kauai has sustained loss of both individual plants and habitat as a result of feral pig activities. Three populations ofI. laurifolium on Oahu are threatened by pigs. Goats are contributing on Kauai to the decline of one population of this plant. Encroaching urbanization and hunting pressure on Oahu tend to concentrate the goat populations in the dry upper slopes of the Waianae Mountains, putting three populations of this plant there under increasing stress. Black-tailed deer threaten half of the known populations of I. laurifolium on Kauai.

Evidence of predation on I. laurifolium by deer is documented on Kauai. Cattle, deer, and goat predation is a possible threat for this plant since it is not known to be unpalatable to these animals.

Military training exercises, troop ground maneuvers, and helicopter landing and drop-off activities on Oahu could trample or flatten I. laurifolium individuals that occur on land leased or owned by the army.

Lantana poses a threat on Kauai to one population of I. laurifolium within Kuia Natural Area Reserve and three other populations on the island. Strawberry guava, a major invader of forests in the Waianae and Koolau Mountains of Oahu, poses an immediate threat to one population of I. laurifolium there. Christmasberry, now a major component of the mesic forests of the Waianae and Koolau Mountains of Oahu, threatens one-third of the I. laurifolium populations there. Thimbleberry poses a threat to two populations of this species on Kauai. Koster's curse threatens one population of I. laurifolium in Oahu's Koolau Mountains; silk oak threatens one population of I. laurifolium in the Waianae Mountains of Oahu.

Conservation and Recovery

The U.S. Army Garrison's Five-year Ecosystem Management Plans to protect endangered species on all of its training areas in the State of Hawaii is devised to prevent range fires and minimize soil erosion. The plans are expected to enhance conservation of the I. laurifolium plants growing on the Schofield Barracks Military Reservation.

One individual of I. laurifolium is found in each of two of the state division of forestry and wildlife's fenced exclosures on Kauai in Mahanaloa Valley and Paaiki Valley.

I. laurifolium has been successfully propagated at Lyon Arboretum's micropropagation laboratory, although outplanting has not yet been attempted.

Contact

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/

Reference

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.