A'e (Zanthoxylum dipetalum var. tomentosum)

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Zanthoxylum dipetalum var. tomentosum

ListedOctober 10, 1996
FamilyRutaceae (Citrus)
DescriptionThornless tree, bears flowers and fruit is an oval follicle.
HabitatMontane mesic forest.
ThreatsDisturbance by animals, competition from alien plant species, volcanic activity, fire.


Zanthoxylum dipetalum var. tomentosum, of the citrus family, is a thornless tree 13-49 ft (4-15 m) tall with a trunk up to 12 in (30.5 cm) in diameter. It has alternate leaves comprised of three to seven leathery, elliptical, gland-dotted, smooth-edged leaflets usually 2.4-12 in (6-30.5 cm) long and 1-5.3 in (2.5-13.5 cm) wide. The undersurface of the leaflets is densely covered with fine, short hairs, and the lowest pair of leaflets is often strongly reduced. The stalks of the side leaflets have one joint each, and the stalk of the terminal leaflet has two joints.

Flowers are usually either male or female, and usually only one sex is found on a single tree. Clusters of five to 15 flowers, 0.4-0.7 in (10-18 mm) long, have a main flower stalk 0.4-1.6 in (10-41 mm) long and individual flower stalks 0.1-0.3 in (2.5-7.5 mm) long. Each flower has four broadly triangular sepals about 0.04-0.06 in (1-1.5 mm) long and two or four yellowish white petals, sometimes tinged with red, 0.2-0.4 in (5-10 mm) long. The fruit is an oval follicle (dry fruit that opens along one side), 0.6-1.3 in (15-33 mm) long, containing one black seed about 0.4-1 in (10-25 mm) long. This variety is distinguished from Z. dipetalum var. dipetalum by the hairs on the undersurface of the leaflets. It is distinguished from other Hawaiian species of the genus by its reduced lower leaflets, the presence of only one joint on some of the leaflet stalks, and the large seeds.

Horace Mann described Z. dipetalum in 1867, and it was named a new variety Z. dipetalum var. tomentosum, based on a specimen he collected at Puu Waawaa on Hualalai, on the island of Hawaii, in 1909. The specific epithet refers to the dense covering of soft hairs on the undersurface of the leaflets. Some authors have placed Hawaiian taxa in the genus Fagara, resulting in F. dipetala var. tomentosa. Nevertheless, Z. dipetalum var. tomentosum is maintained in the current treatment of the Hawaiian species.


Z. dipetalum var. tomentosum grows in degraded 'ohi'a-dominated montane mesic forest, often on aa lava, at elevations of 3,000-3,400 ft (910-1,040 m). Associated species include mamane, lama, 'ala'a, 'iliahi, 'ohe, kolea, and kopiko.


Only one population of Z. dipetalum var. tomentosum has ever been known, located at Puu Waawaa on Hualalai, on the island of Hawaii. At the end of the twentieth century, approximately 24 individuals were known, scattered through the area.


Threats to Z. dipetalum var. tomentosum include browsing, trampling, and habitat disturbance by cattle, feral pigs, and sheep; competition from alien plant species, such as kikuyu grass, fountain grass, lantana, koa haole, and silk oak; habitat change due to volcanic activity; and fire. In addition, the species is threatened by a risk of extinction from naturally occurring events and/or reduced reproductive vigor due to the small number of existing individuals in only one population.

Conservation and Recovery

The State of Hawaii's Division of Forestry and Wildlife has out-planted approximately 20 individuals onto state-owned land in the Puu Waawaa area. This land is not fenced and is currently under lease as a pasture. No other species-specific efforts are underway.


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


U. S. Fish and Wildlife Service. 1998. "Big Island II: Addendum to the Recovery Plan for the Big Island Plant Cluster." U. S. Fish and Wildlife Service, Portland, Oregon, 80 pp.