Dwarf Iliau

Wilkesia hobdyi

Description

Wilkesia hobdyi, commonly known as dwarf iliau, is a shrub in the aster family that stands about 2 ft (0.6 m) tall and branches from the base. The tip of each branch possesses a tuft of narrow leaves that are about 0.5 in (1.3 cm) wide and 2.8-5.9 in (7.1-15 cm) long. The whorled leaves are joined together in a short sheathing section at their bases. The flower-heads are arranged in clusters about 9.8-17.7 in (24.9-50 cm) long. Each head is cream colored and about 0.75 in (1.9 cm) in diameter.

This species is likely pollinated through out-crossing and is probably self-incompatible. Insects are the most likely pollinators. Reproduction and seedling establishment are occurring and appear sufficient to sustain the populations. Flowering has been observed most often in the winter months but also during June. Fruits may be dispersed when they stick to the feathers of birds. Densities reach one plant per square yard (per 0.8 sq m) in localized areas, and hybridization with W. gymnoxiphium may be occurring.

Habitat

W. hobdyi grows in degraded cliff sites and very dry ridges at elevations of 90-1,300 ft (27.4-396.2 m). Most populations are surrounded by shrubby alien vegetation such as koa haole, lantana, and sourbush; however, the associated native vegetation includes Myoporum sandwicense (naio), Sida fallax (ilima), Waltheria indica (aalii), and Eragrostis variabilis.

Distribution

The W. hobdyi population at Polihale Ridge on the island of Kauai is believed to contain 250-300 plants. A population of about 100 individuals of the species was discovered in 1982 on the adjacent Kaaweiki Ridge. A third population, estimated at 10-50 individuals, was discovered on a cliff face in Waiahuakua Valley six years later. There are additional populations of 50 plants at Makaha and 10 plants at Pohakuao. These five populations (about 420-510 total individuals) on state-owned land comprise all the W. hobdyi plants known.

Three additional and unconfirmed observations, which may be of this species, have been reported. The observations were made from a distance with binoculars. The first observation was made in the Nualolo-Aina Valley by the state botanist during a survey of the Na Pali Coast in 1979. This population comprised about 10 plants. The plants were not seen during a follow-up survey of the area five years later, and the observer stated that the species may be a good indicator plant for the presence of grazing animals. The second observation was that of a single plant on a cliff wall in Milolii Valley along Na Pali Coast in 1980, and the plant was not seen during a subsequent survey in 1989. The third observation, made on March 6, 1991, was of an estimated 30-40 plants seen with binoculars on Haeleele Ridge, the ridge south of Polihale Ridge. The known populations and the unconfirmed sightings are all from the nearly vertical rock outcrops on the Na Pali Coast of western Kauai. There are at least two other species of plants in this area that—from a distance— superficially resemble W. hobdyi; it is not known how it was determined that the observations were of W. hobdyi.

Threats

The greatest immediate threats to the survival of this species are habitat disturbance and browsing by feral goats. The goats' activities in the area accelerate erosion and facilitate the encroachment of competing naturalized plants. Although the low number of individuals and their restricted habitat could be considered a potential threat to the survival of the species, the plant appears to have vigorous reproduction and should survive indefinitely if goats are eliminated from its habitat.

Conservation and Recovery

W. hobdyi has been successfully propagated and grown in cultivation by National Tropical Botanical Garden, where seeds are in storage and plants are growing under protected conditions. The Kauai District Division of Forestry and Wildlife has out-planted 20 individuals of this taxon at Kalepa and Nounou Forest Reserves, and additional outplanting of this species is planned for an enclosure at Haeleele Ridge in Puu Ka Pele Forest Reserve.

Contacts

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/

Pacific Remote Islands Ecological Services Field
Office
300 Ala Moana Blvd., Room 3-122
P.O. Box 50088
Honolulu, Hawaii 96850
Telephone: (808) 541-1201
Fax: (808) 541-1216

Reference

U.S. Fish and Wildlife Service. 1995. "Recovery Plan for the Kauai Plant Cluster." U.S. Fish and Wildlife Service, Portland, Oregon. 270 pp.