Amaranthus brownii

No Common Name

Description

Amaranthus brownii, an annual herb of the amaranth family (Amaranthaceae), has leafy upright or ascending stems that are 1-3 ft (0.3-0.9 m) long. The alternate leaves, 1.6-2.8 in (4-7 cm) long and 0.06-0.16 in (0.1-0.14 cm) wide, are long, narrow, slightly hairy, and more or less folded in half lengthwise. Flowers are either male or female, and flowers of both sexes are found on the same plant. The green flowers are subtended by two oval, bristle-tipped bracts about 0.04 in (1 mm) long and 0.03 in (0.7 mm) wide. Each flower has three bristle-tipped sepals. These are lance-shaped and 0.05 in (1 mm) long by 0.03 in (0.7 mm) wide in male flowers. Female flowers have spatula-shaped sepals that are about 0.03 in (0.7 mm) long by 0.01 in (0.2 mm) wide. Male flowers have three stamens; female flowers have two stigmas. The flattened oval fruit, approximately 0.03 in (0.7 mm) long and 0.02 in (0.5 mm) wide, does not split open at maturity to reveal its one lens-shaped, reddish black seed. This species can be distinguished from other Hawaiian members of the genus by its spineless leaf axils, its linear leaves, and the aforementioned fruit that does not split open at maturity.

A. brownii is an herbaceous annual with a growing season that extends from December to June or July. Plants in an early stage of flowering have been observed in February, and seed from dead plants have been collected during June. Phenology may vary somewhat from year to year, depending on rainfall and climatic factors. The means of pollination are unknown.

A. brownii was first collected by Edward L. Caum during the Tanager Expedition in 1923. Erling Christophersen and Caum named it in honor of Dr. F. B. H. Brown eight years later.

Habitat

A. brownii typically grows on rocky outcrops in fully exposed locations at elevations between 100 and 800 ft (30 and 244 m). Associated species include 'aheahea, kakonakona, and kupala.

Distribution

A. brownii is the rarest native plant on Nihoa. When it was first collected in 1923, it was considered most common on the ridge leading to Miller's Peak, although also abundant on the ridges to the east. The two groupings of colonies known in recent years, separated by a distance of 0.25 mi (0.4 km), contained a total of approximately 35 individuals in 1983—23 plants at Miller's Peak and about 12 plants in three small colonies in Middle Valley. No plants have been seen at either location since 1983, even though U. S. Fish and Wildlife Service (FWS) staff have surveyed for them annually. However, none of the surveys since 1983 have been done during the winter, when these annuals are easiest to find and identify. It will be necessary to conduct winter surveys in order to get an accurate population count and collect seeds or cuttings to establish cultivated populations.

Individuals of A. brownii are difficult to distinguish from other desiccated herbaceous or seedling plants during the dry summer months, when surveys are conducted. The unusually dry conditions of the past several years are another probable factor for this species not being reported.

December through March is the normal growing season for A. brownii, but the seas are too rough during these months to permit landing on Nihoa by survey personnel. The FWS continues to attempt winter surveys of Nihoa with veteran field botanist Steve Perlman of the Hawaii Plant Conservation Center, who believes that the species is likely present during the wetter winter months.

Threats

Pigweed, an invasive alien species, is widespread on Nihoa and grows in habitat similar to A. brownii.

Because it grows on rocky outcrops, A. brownii is more likely to be affected by substrate changes. Due to the small numbers of populations and individuals and its limited distribution, this species is threatened by extinction from naturally occurring events and through reduced reproductive vigor. This species may have experienced a reduction in total numbers due to disturbances resulting from Polynesian settlement of Nihoa.

The very limited range and small populations of
A. brownii greatly increase the potential for extinction from stochastic events. A. brownii has only four colonies and is believed to number fewer than 40 individuals. The limited gene pool of these species may severely depress its reproductive vigor.

Conservation and Recovery

A. brownii seeds have been collected for cultivation, but resulting germination and survival rates were very low. This may indicate a reduction in the reproductive vigor of the species. There are no known plants or seeds in any botanical collection.

Immediate recovery actions should include a winter expedition to monitor and map remaining populations and to collect seeds and cuttings to establish cultivated populations. Micropropagation techniques developed at the Lyon Arboretum in Honolulu offer probably the best prospect for culturing sufficient material to establish protected off-site populations that can later be used to reestablish A. browniiin the wild.

Increasing the numbers of plants and locations of this species on Nihoa will be critical to its ultimate survival and recovery. Considerable work will need to be done to identify, prepare, protect, and monitor sites for establishing new wild populations, particularly if the sites are outside of the historic range. Necker Island should be considered since it is adjacent to Nihoa, has similar habitat, and is protected as a FWS refuge. Kilauea Point and Midway Atoll National Wildlife Refuges should also be assessed for suitability since they are protected areas, have plant nursery facilities, and have a full time staff.

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
(503) 231-6121
http://pacific.fws.gov/

U. S. Fish and Wildlife Service
Pacific Islands Ecoregion
Pacific Islands Fish and Wildlife Office
300 Ala Moana Boulevard, Room 3-122
Box 50088
Honolulu, Hawaii, 96850
Telephone: (808) 541-3441
Fax: (808) 541-3470

Reference

U.S. Fish and Wildlife Service. 21 August 1996. "Endangered and Threatened Wildlife and Plants: Endangered Status for Three Plants From the Island of Nihoa, Hawaii." Federal Register 61 (163): 43178-43184.