A'e (Zanthoxylum hawaiiense)

views updated


Zanthoxylum hawaiiense

ListedMarch 4, 1994
FamilyRutaceae (Citrus)
DescriptionSmall to medium thornless tree with lemon-scented, toothed leaflets and clusters of 15-20 flowers.
Habitat'Ohi'a-dominated lowland dry or mesic forests, often on lava.
ThreatsCompetition from alien plants; habitat destruction by cattle, goats, and sheep; limited numbers.


Zanthoxylum hawaiiense (a'e) is a thornless tree usually 10-26 ft (3-7.9 m) tall with a trunk up to 10 in (25.4 cm) in diameter. It has alternate leaves comprising three leathery, triangular-oval or lance-shaped, gland-dotted, lemon-scented, toothed leaflets usually 1.3-3.9 in (3.3-9.9 cm) long and 0.6-2 in (1.5-5.1 cm) wide. The stalk of each of the two side leaflets has one joint, and the stalk of the terminal leaflets has two joints.

Flowers are usually male or female, and typically only one sex is found on a single tree. Clusters of 15-20 flowers 1.6-3.1 in (4.1-7.9 cm) long have a main flower stalk 0.8-2 in (2-5.1 cm) long and individual flower stalks 0.08-0.2 in (2-5 mm) long. Each flower has four narrowly triangular sepals about 0.04 in (1 mm) long and four hairless petals (possibly absent in male flowers) of an unknown color. The fruit is a sickle-shaped follicle (dry fruit that opens along one side) 0.3-0.4 in (8-10 mm) long, containing one black seed about 0.3 in (8 mm) in diameter. This species is distinguished from other Hawaiian species of the genus by 1) its leaves, which are always made up of three leaflets of similar size; 2) the presence of only one joint on some of the leaf stalks; and 3) the shorter follicle with a rounded tip.


A'e typically grows in 'ohi'a-dominated lowland dry or mesic forests, often on lava, at elevations of 1,800-5,710 ft (549-1,740 m). Associated species include hame, on Kauai; hala pepe, on Molokai; a'ia'i, on Maui; and mamane and naio, both on the island of Hawaii.


Historically, this species was found only on the island of Maui on the western slope of Haleakala; and on the island of Hawaii in the Kohala Mountains, the northwestern slopes of Mauna Kea and Mauna Loa, and the slopes of Hualalai.

Since 1975 Z. hawaiiense has been identified as extant on at least four of the five islands on which it originally occurred, with at least 11 known populations and more than 250 individuals. On Kauai, one extant individual is found in Waimea Valley. On Molokai, at least two populations occurone in Pelekunu Valley and one near Puu Kolekole. On eastern Maui, three extant populations are located at Auwahi, Lualailua, and Kanaio. On the Big Island, five populations are located at Puu Waawaa and the Pohakuloa Training Area. In addition, numerous individuals have been located between Puu Waawaa and Pohakuloa Training Area, and on the western periphery of Pohakuloa Training Area. The new populations bring the total number of individuals to more than 250.


Feral and domestic animals are major threats to this species. Browsing, grazing, and trampling by feral goats (Molokai, Maui, Hawaii), sheep (Hawaii), pigs (Hawaii), and cattle (Maui) have resulted in habitat destruction and have opened new sites to alien plant invasion. Introduced weedy species such as Melia azedarach (chinaberry), Lantana camara (lantana), Pennisetum clandestinum (kikuyu grass), and P. setaceum (fountain grass) compete with seedlings for light, space, and nutrients, often precluding the establishment of successive generations. Fire is another potential danger to Z. hawaiiense, although its response to fire is unknown.

Conservation and Recovery

The National Tropical Botanical Garden has propagated the a'e. The newly observed plants near Puu Waawaa and at Pohalmloa Training Area appear healthy and are flowering and fruiting. The individuals found in 1921 in Hawaii Volcanoes National Park were not present in 1967 and were not seen during surveys in 1992-94. Seeds were germinated by staff at Colorado State University in 1991-93. Individuals grow well in the greenhouse setting.

Propagation and maintenance of ex situ genetic stock should continue. Habitat of existing populations should be protected from feral ungulates and managed for alien plant control. Steps should be taken to ensure that populations remain viable on each of the four islands on which the species presently occurs.


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

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


U. S. Fish and Wildlife Service. 4 March 1994. "Endangered and Threatened Wildlife and Plants; Determination of Endangered or Threatened Status for 21 Plants from the Island of Hawaii, State of Hawaii." Federal Register 59 (43): 10305-10325.