'Oha (Delissea rivularis)
|Listed||October 10, 1996|
|Description||Shrub with hairy stems; leaves arranged in a rosette.|
|Habitat||Near streams on steep slopes in 'ohi'a-'olapa montane wet or mesic forests.|
|Threats||Competition with the encroaching alien plant prickly Florida blackberry; habitat destruction by feral pigs.|
Delissea rivularis, also known as 'oha, a shrub with hairy stems in the bellflower family, is un-branched or branched near the base and grows to a height of 13-16 ft (3.9-4.8 m). The leaves are arranged in a rosette at the tips of the stems. The elliptic to lance-shaped leaves are 8-12 in (20.3-30.5 cm) long and 1.2 to 3.2 in (3-8.1 cm) wide, with minutely toothed margins. Both leaf surfaces are covered with hairs. Six to 12 flowers are arranged on an inflorescence stalk 1.6-3.2 in (4-8.1 cm) long, each having an individual stalk 0.4-0.6 in (1-1.5 cm) in length. The curved and hairy flowers, white with blue longitudinal stripes, are 1.2-1.6 in (3-4 cm) long and have one dorsal knob. The fruit is a spherical, dark purple berry 0.4-0.6 in (1-1.5 cm) in diameter. This species is distinguished from others of the genus by the color, length, and curvature of the corolla; shape of the leaves; and presence of hairs on the stems, leaves, flower clusters, and corolla.
D. rivularis is found near streams on steep slopes in 'ohi'a-'olapa montane wet or mesic forests. Associated native species include kanawao, Athyrium sp., Carex sp., Coprosma sp. (pilo), and Sadleria sp. ('ama'u).
D. rivularis had historical occurrences on Kauai at an unknown location near Waiakealoha waterfall, Waialae Valley, Hanakoa Valley, and Kaholuamano. This species, recently recollected after almost 80 years, is now known only from the upper Hanakoa Valley stream area of northwestern Kauai. This population of 15-20 plants, scattered over an area of more than 1,100 sq ft (102.2 sq m), is on sate land within the Hono O Na Pali Natural Area Reserve at about 3,900 ft (1,188.7 m) in elevation.
The major threats to D. rivularis are competition with the encroaching alien plant prickly Florida blackberry, habitat destruction by feral pigs, and reduced reproductive vigor and a risk of extinction from naturally occurring events due to the small number of remaining individuals in the single remaining population. It is probable that rats eat the fruit. Erosion, landslides, rock slides, and other natural events that kill individual plants and destroy habitat are especially dangerous threats to this species.
Conservation and Recovery
Seeds are being stored at the National Tropical Botanical Garden, and the Lyon Arboretum has propagated stock by tissue culture.
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. 1988. "Kauai II: Addendum to the Recovery Plan for the Kauai Plant Cluster." U.S. Fish and Wildlife Service, Portland, Oregon. 84 pp.