Nanu

Gardenia mannii

Description

Gardenia mannii, or nanu, is a tree in the coffee family (Rubiaceae) that can reach 50 ft (15.2 m) in height. The leaves are inversely lance-shaped or slightly more elliptic, 2.4-10.6 in (6.1-26.9 cm) long, and 1.4-4 in (3.5-10.1 cm) wide. The upper leaf surface is sticky. The fragrant flowers bloom in the late afternoon, usually lasting for two days. G. mannii has been observed in flower and fruit in June and September; these growths are solitary and occur at the branch tips. The cup-shaped calyx, 0.1-0.2 in (0.25-0.5 cm) long, extends into four to six leathery, long, thin, and terminal hollow appendages called spurs. These spurs are linear spatula-shaped, S-shaped, or, rarely, sickle-shaped, 0.9 to 1.8 in (2.2-4.5 cm) long, and 0.2 to 0.4 in (0.5-1 cm) wide. The corolla is cream colored on the outside and white on the inside. The tubular portion of the flower is 0.7-1.1 in (1.7-2.8 cm) long (when dry), and the seven to nine lobes are 0.6-0.9 in (1.5-2.2 cm) long (when dry). The yellow to orange fruit is broadly elliptic. This species is distinguished from others in the genus by the shape and number of the calyx spurs.

G. mannii was first described by Harold St. John and J.R. Kuykendall in 1949 from a specimen they had collected a few years earlier in the Koolau Mountains. In the same paper, St. John and Kuykendall also described G. mannii var. honoluluensis, which is not currently recognized. The specific epithet honors Horace Mann Jr., an early collector of Hawaiian plants.

Habitat

G. mannii is usually found on moderate to moderately steep gulch slopes 980-2,460 ft (298.7-749.8 m) in elevation. 'Ohi'a codominates in mesic or wet forests with a mixture of native plants such as alaa, koa, and uluhe. Other associated plants include kalia, hoio, alani, hoawa, ohe mauka, hame, kanawao, pilo, kawau, maile, and kopiko.

Distribution

G. mannii was known historically on Oahu from seven widely scattered populations in the Waianae Mountains and 39 populations distributed along almost the entire length of the Koolau Mountains. Twenty-three populations of G. mannii are currently distributed along a 26-mi (41.8-km) length of the Koolau Mountains, from Kaunala Gulch and Kaunala-Waimea Ridge at the northernmost extent of its range to Palolo at the southernmost extreme. In the Waianae Mountains, this species is now found in five populations over a four-mile distance from north Haleauau Valley to Kalnaa Gulch. These 28 extant populations occur on private land, including the Nature Conservancy of Hawaii's Honouliuli Preserve and land leased by the Department of Defense for Kawailoa and Kahuku Training Areas; City and County of Honolulu land; state land; and federal land on Schofield Barracks Military Reservation. The existing populations in 1997 totaled 70-100 individuals, with 23 of the 28 populations each containing five or fewer individuals.

Threats

G. mannii is threatened by habitat degradation and destruction by feral pigs; potential impacts from military activities; competition with alien plants such as Koster's curse, prickly Florida blackberry, and strawberry guava; potential fire; and risk of extinction from unpredictable natural events or reduced reproductive vigor due to the small number of widely dispersed remaining individuals. This species is also potentially threatened by predation from rats. The Kapakahi Gulch population also is threatened by the black twig borer.

Conservation and Recovery

Because of the impossibility of hunting due to dangers associated with unexploded ordnance, the U. S. Army is experimenting with leg snaring to control pig populations in areas adjacent to G. mannii individuals in Schofield Barracks Military Reservation, West Range.

The Lyon Arboretum and the National Tropical Botanical Garden have successfully propagated G. mannii, and seeds are in storage at the National Tropical Botanical Garden.

Enclosures should be constructed around the known populations of G. mannii to reduce impacts from feral pigs. Subsequent control or removal of pigs from these areas will alleviate their impact on native ecosystems. Additionally, specific efforts should be made to immediately fence, weed, and otherwise protect the 23 populations that have only a few remaining individuals. A commitment should be developed for long-term stewardship and servation of all of these areas once they have been enclosed.

The black twig borer has been identified as a threat to one population of G. mannii. It is not known how this plant will be affected by defoliation or reduced vigor due to infestations of this alien insect. A number of parasitoids have been introduced to control the beetle, though none of them has become established. Further research on biological control of the beetle will need to proceed cautiously as a number of rare native Hawaiian scolyfids are closely related to the black twig borer.

A coordinated fire protection plan for endangered plant species on City and County of Honolulu, federal (Schofield Barracks Military Reservation), and private (Honouliuli, Kawailoa, and Kahuku Training Area) lands needs to be developed and implemented.

Populations of this species are seriously threatened by rat predation. A rat control plan should be developed and implemented. This should include the use of the currently approved Diphacinone bait blocks and ultimately a more broadscale method such as aerial dispersal of rodenticide.

Contact

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

Reference

U.S. Fish and Wildlife Service. 1998. "Recovery Plan for Oahu Plants." U.S. Fish and Wildlife Service, Portland, Oregon, 207 pp., plus appendices.