Vigna o-wahuensis

No common name

Description

Vigna o-wahuensis, a member of the pea family, is a slender twining annual or perennial herb with fuzzy stems that grow to 1.3 ft (0.4 m) in length. The leaves are each comprised of three leaflets, 0.5-3 in (1.3-7.6 cm) long and 0.04-1 in (1-25 mm) wide, that are varied in shape from round to linear and are sparsely or moderately covered with coarse hairs. Flowers, in clusters of one to four, have thin, translucent, and pale yellow or greenish yellow petals about 0.8-1 in (2-2.5 cm) long. The two lowermost petals are fused and appear distinctly beaked. The sparsely hairy calyx is 0.2-0.3 in (5-7 mm) long with asymmetrical lobes that measure about 0.1 in (2.5 mm) long. The fruits are long slender pods 1.6-3.5 in (4-9 cm) long and about 0.2 in (5 mm) wide that may or may not be slightly inflated, each containing seven to 15 gray to black seeds less than 0.2 in (5 mm) long. This species differs from others in the genus by its thin yellowish petals, sparsely hairy calyx, and thin pods which may or may not be slightly inflated. V. o-wahuensis was described by T. Vogel in 1836 from a specimen collected in the Waianae Mountains of Oahu. Gray described another species, V. sandwicensis, for which Rock later designated two varieties: var. heterophylla and var. sandwicensis (Rock 1920). The currently accepted treatment places V. sandwicensis in synonymy under V. sandwicensis, in 1854, from which Rock later designated two varieties: var. heterophylla and var. sandwicensis. The currently accepted treatment places V. sandwicensis in synonymy under V. o-wahuensis.

Habitat

V. o-wahuensis occurs in dry to mesic grassland and shrubland from 30-4,500 ft (9-1,310 m) in elevation. Other associated plant species include 'ilima, Chenopodium ('aheahea), Dubautia menziesii, and Osteomeles anthyllidifolia.

Distribution

V. o-wahuensis was known historically from Niihau and from an unspecified location on Kauai. The species was known on Oahu from between Waimanalo and Makapuu Point, the Mokulua Islets, and the Waianae Mountains. On Maui, V. o-wahuensis was known from Makawao and Waiakoa on East Maui. There are no currently known populations on Niihau, Kauai, Oahu, or Maui. V. o-wahuensis was known historically on Molokai from the western end of the island in the vicinity of Ilio Point. On Lanai, this species had historical occurrences at scattered locations across the island's southern half and at Kanepuu. V. o-wahuensis was also known from Kau on the island of Hawaii.

The seven extant V. o-wahuensis populations on the islands of Molokai, Lanai, Kahoolawe, and Hawaii totaled less than 100 individuals in 1995. Molokai has two populations separated by a distance of 2.5 mi (4 km). One population, south of Onini Gulch at about 2,800 ft (853 m) elevation on privately owned land, covers an area of 200 sq ft (18.5 sq m) in a forestry planting of tropical ash and pine; the other population of about ten individuals is on privately owned land at Makolelau. At least one individual of V. o-wahuensis is known on Lanai from the arid windward slopes northeast of Kanepuu above Lapaiki at about 1,200 ft (366 m) elevation on privately owned land. On the state-owned island of Kahoolawe, one V. o-wahuensis plant grows in pili grassland at 460 ft (140 m) elevation between Makaalae and Lua Kealialalo. Near the summit at around 1,300 ft (400 m) elevation, about 20 plants grow in a 100 sq ft (9 sq m) area with a few more plants scattered nearby. The size of the population, about 0.5 mi (0.8 km) south of Hanakanaea near "Sailor's Hat," has not been determined, but at least one collection was made in 1995. On the island of Hawaii, V. o-wahuensis is known only from Nohonaohae Cinder Cone on privately owned land. Ten plants are known from aalii lowland dry shrubland within an exclosure containing pasture grass.

Threats

The primary threats to V. o-wahuensis are habitat degradation by pigs and axis deer, competition with various alien plant species, fire, and critical loss of reproductive vigor due to the small number of existing populations and individuals.

One population of V. o-wahuensis on Molokai is threatened by pigs. Axis deer threaten one population of this species above Lapaiki at Kapoho on Lanai. V. o-wahuensis is not known to be unpalatable to cattle, deer, and goats; as such, predation is a probable threat to this plant at sites where these animals have been reported.

All populations of V. o-wahuensis on Molokai are being negatively affected by molasses grass. Fountain grass threatens the native vegetation on the leeward slopes of Hualalai in a region where the only known Hawaii island population of V. o-wahuensis exists. The primary alien plant threat to V. owahuensis on Kahoolawe is kiawe, although the populations of this species on the island have also been harmed by koa haole and buffelgrass. Fire is a threat to one population of this plant on Molokai and all known populations of V. o-wahuensis on Kahoolawe.

Conservation and Recovery

V. o-wahuensis has been successfully propagated, and one individual exists in cultivation at the University of Hawaii's Volcano Rare Plant Facility, where it has flowered. Seed germination tests indicate 52% germination of fresh seeds and less than 10% germination after a minimum of 45 days in storage. Less than 100 seeds are in storage at the National Tropical Botanical Gardens.

Contact

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Eastside Federal Building
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 November 1994. "Endangered Status for 12 Plants From the Hawaiian Islands." Federal Register 59 (217): 56333-56351.