No Common Name
|Listed||September 20, 1991|
|Description||Tall, grasslike sedge with solid stems and spirally arranged flowers.|
|Habitat||Lowland wet forest.|
|Threats||Low numbers, tourist development, alien plant species.|
Gahnia lanaiensis, a member of the sedge family (Cyperaceae), is a tufted, perennial, grasslike plant that ranges in height from 4.9-9.8 ft (1.5-2.9 m). This sedge may be distinguished from grasses and other genera of sedges on Lanai by its spirally arranged flowers, its solid stems, and its numerous, three-ranked leaves. G. lanaiensis differs from the other members of the genus on the island by its achenes (seedlike fruits), which are 0.14-0.18 in (3.6-4.6 mm) long and purplish black when mature. July has been regarded as the end of the flowering season for G. lanaiensis. Plants of this species have been observed with fruit in October.
The habitat of G. lanaiensis is lowland wet forest, ranging from shrubby rainforest to open scrubby fog belt or degraded lowland mesic forest. The plant occurs on flat to gentle ridge-crest topography in moist to wet clay or other soil substrate at elevations of approximately 3,080-3,380 ft (939-1,030 m) in open areas or in moderate shade. Associated native species include native mat ferns, shrubs, and trees—Metrosideros, Dicranopteris, and Diplopteryqium shrubland with Sadleria, Coprosma, Lycopodium, Scaevola, and Styphelia —as well as alien species.
G. lanaiensis is endemic to Lanai, although fewer than 50 large plants in four populations along the summit ridges of Lanaihale at 3,000-3,400 ft (914-1,036 m) in elevation were known in 1991. This distribution encompasses the entire known historic range of the species. Seeds were collected from all four known populations in 1991.
The primary threats to G. lanaiensis are the small number of plants and its restricted distribution, which increases the potential for extinction from stochastic events.
Manuka, a weedy tree introduced from New Zealand, dominates the overstory above the population of about 20 G. lanaiensis plants at the Lanai-hale summit, and it appears likely to start competing with Gahnia for space. Strawberry guava, firetree, sourbush, molasses grass, Rubus rosifolius, Paspalum conjugatum, and Tibouchina are other major invaders that clearly pose threats to G. lanaiensis. Disturbance by deer exacerbates the alien plant invasion problem.
Axis deer have invaded the ridgetop habitat of this species and directly, through browsing and trampling, and indirectly, through opening up avenues for invasion of alien plants by their foraging activities, pose a threat to the continued existence of the species.
Since perhaps as many as half the known individuals of this species grow adjacent to the Munro Trail that crosses Lanaihale, this threat must be considered serious.
Conservation and Recovery
The Hawaii Plant Conservation Center had in storage a total of 1,300 seeds from G. lanaiensis from Lanai as of August 1992.
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
National Wildlife Refuge Complex
Hawaii and Pacific Islands
300 Ala Moana Boulevard, Room 5302
Honolulu, Hawaii 96850-0052
Telephone: (808) 541-1201
Fax: (808) 541-1216 Mailing Address:
P.O. Box 50167
Honolulu, Hawaii 96850-5000
Cuddihy, L. W. and C. P. Stone. 1990. Alteration of Native Hawaiian Vegetation: Effects of Humans, Their Activities and Introductions. University of Hawaii Cooperative National Park Resources Study Unit, Honolulu.
Wagner, W. L., D. R. Herbst, and S. H. Sohmer. 1990.Manual of the Flowering Plants of Hawai'i. University of Hawaii Press and Bishop Museum Press, Honolulu.