No Common Name
|Listed||February 25, 1994|
|Description||Medium-size tree with a straight, gray trunk and spreading branches; elliptical leaves; and pale yellow flowers.|
|Habitat||Steep exposed cliffs or ridge slopes in coastal to lowland mesic forests.|
|Threats||Competition from alien plants, feral goats, insects, overcollecting, limited numbers.|
Munroidendron racemosum is a tree in the ginseng family (Araliaceae). It grows to about 23 ft (7 m) and has a straight gray trunk crowned with spreading branches. The leaves are 6-12 in (15-30.5) long and comprise five to nine oval or elliptical leaflets with clasping leaf stalks. Each leaflet is 3-7 in (8-17 cm) long and usually 1.6-3.9 in (4-10 cm) wide. About 250 pale yellow flowers are borne along a stout hanging stalk 10-24 in (25.4-61 cm) long. Each flower has five or six lance-shaped petals 0.3-0.4 in (long, emerging from a cup-shaped or ellipsoid calyx tube). Both the lower surface of the petals and the calyx tube are covered with whitish scaly hairs. The fruit is an egg-shaped drupe 0.3-0.5 in (0.8-1.3 cm) long and nearly as wide, situated atop a flat, dark red disk (stylopodium). This species is the only member of a genus endemic to Hawaii, differing from other closely related Hawaiian genera of the family primarily in its distinct flower clusters and corolla.
Some reproduction is occurring, with flowering and fruiting occurring throughout the year. Self-pollination is assumed to occur due to viable seed produced by isolated individuals. Pollinators have not been observed, but insect pollination is likely. Dispersal mechanisms are unknown.
Most M. racemosum populations are found on steep exposed cliffs and ridge slopes in coastal to lowland mesic forests. A few populations are found in mesic hala forests, lantana-dominated shrubland, or Eragrotis grasslands. Associated plants include common guava (Psidium guajava), kopiko (Psycho-tria spp.), kukui (Aleurites moluccana), and lama.
M. racemosum has historical occurrences at scattered locations throughout the island of Kauai. Fifteen populations are now found at elevations of 390-1,310 ft (119-400 m) on private and state land along the Na Pali Coast within the Na Pali Coast State Park and Hono O Na Pali Natural Area Reserve, in the Poomau and Koaie branches of Waimea Canyon, in the Haupu Range area, and on Nounou Mountain.
Although populations are widely distributed, most of them number only one or two individuals. The largest population has fewer than 50 individuals. There are only an estimated 200 M. racemosum trees left.
Competition with introduced plants is the major threat to M. racemosum. Kukui and ti plants, introduced by Polynesian immigrants to the Hawaiian Islands, compete with this species for space in the forests of Kauai. Other introduced plants threatening M. racemosumhabitat include chinaberry (Melia azedarach ), common guava, firetree (Myrcia faya ), koa haole (Leucaena leucocephala ), lantana (Lantana camara ) and Sacramento burr. Several animal species also pose threats to M. racemosum. Feral goats degrade the habitat, and cattle were formerly present in areas where the trees grow. Predation of the trees' fruits by rats is probable. An introduced insect of the longhorned beetle family, which killed a mature cultivated tree, has the potential of affecting wild trees. In addition, because each population of this species contains only one or a few trees, the species is threatened by humans through overcollecting for scientific or horticultural purposes. These practices could lead to stochastic extinction, and reduced reproductive vigor. Fire also endangers M. racemosum.
Conservation and Recovery
M. racemosum has been successfully propagated and cultivated by Lyon Arboretum, the National Tropical Botanical Garden, and Waimea Arboretum. In 1995, Lyon Arboretum had seed in the tissue culture lab and five plants on arboretum grounds. The National Tropical Botanical Garden, as of the same year, was holding seeds in storage and had plants growing in their garden. Waimea Arboretum was maintaining three plants at this time.
The Division of Forestry and Wildlife has out-planted about 400 individuals at Kauhao Ridge and other populations at Haeleele Ridge in Puu Ka Pele Forest Reserve.
Pacific Joint Venture
300 Ala Moana Boulevard, Room 3-122
P.O. Box 50167
Honolulu, Hawaii 96850-0056
U.S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Eastside Federal Complex
911 N.E. 11th Ave.
Portland, Oregon 97232-4181
U.S. Fish and Wildlife Service. 25 February 1994. "Endangered and Threatened Wildlife and Plant; Determination of Endangered or Threatened Status for 24 Plants from Island of Kauai, HI." Federal Register 59 (38): 9304-9329.