Agrimony Sandbur

Cenchrus agrimonioides

Description

Cenchrus agrimonioides, also called kamanomano or agrimony sandbur, is a perennial grass with stems 1-6.7 ft (0.3-2 m) in height. The leaf blades, 8-16 in (20.3-40.6 cm) long and 0.2-1 in (5.1-25.4 mm) wide, are flat or folded and have a prominent midrib. The inflorescence (flower cluster) is a raceme (an unbranched inflorescence with flowers arranged along the axis) 2-4 in (5.1-10.2 cm) long, bearing cylindrical to lance-shaped burs 0.3-0.7 in (7.6-17.8 mm) long. The burs are densely hairy with an outer series of numerous, somewhat spreading, bristles. Each bur partially envelops one spikelet or ultimate flower cluster. This species is distinguished from others in the genus by the cylindrical to lance-shaped bur and the arrangement and position of the bristles. C. agrimonioides var. agrimonioides differs from var. laysanensis in generally having smaller burs, shorter stems, and narrower leaves.

Louis C. A. von Chamisso, a botanist on the Russian vessel Rurik, first collected C. agrimonioides on Oahu during a world expedition between 1816 and 1817. Carl Bernhard von Trinius described the species several years later. Other published names considered synonymous with C. agrimonioides include C. calyculatus var. uniflorus, C. laysanensis, and C. pedunculatus. The two currently recognized varieties are the nominate variety and variety laysanensis, which was described by F. B. Brown in 1931.

Habitat

C. agrimonioides var. agrimonioides is usually found on dry rocky ridges or slopes, or on ridges in mesic 'ohi'a-koa forest from 1,830-2,700 ft (558-823 m) in elevation. Associated plant taxa include Alyxia oliviformis (maile), Psydrax odoratum (alahe'e), Carex sp., Diospyros sp. (lama), and Eragrostis variabilis.

Distribution

C. agrimonioides var. agrimonioides was known historically from the Waianae Mountains of Oahu, Kaaukuu on Lanai, and the south slope of Haleakala and Ulupalakua on Maui. It may possibly have occurred on the island of Hawaii; undocumented observations of this species have been reported from unspecified locations on this island.

C. agrimonioides var. agrimonioides is currently known from Oahu and Maui. A 1997 total of 27-28 plants survived in the Waianae Mountains of Oahu in the following populations: three to four individuals occurred at Pahole Gulch in the Pahole Natural Area Reserve, about ten at Makaha-Waianae Kai Ridge in Honolulu, three at Kahanahaiki Valley, two on the central ridge of Makua on the U.S. Army's Makua Military Reservation, six in east Makaleha on state land, and two individuals in Pualii drainage on private land in the Nature Conservancy's Honouliuli Preserve. A 10-sq ft (0.9-sq m) patch of C. agrimonioides var. agrimonioides plants is known on Maui from state land within Kanaio Natural Area Reserve. The number of individuals statewide totaled fewer than 100 in 1997.

The other variety of this species, C. agrimonioides var. laysanensis, was known historically from the northwestern Hawaiian islands of Laysan, Kure, and Midway, all within the Northwestern Hawaiian Islands National Wildlife Refuge. This variety has not been seen since 1973. These islands are infrequently surveyed for plants, the last comprehensive survey being completed in the 1980s, so it is possible that the variety still exists and will be found with further survey efforts.

Threats

The major threats to C. agrimonioides var. agrimonioides are habitat degradation and destruction on Oahu by feral pigs, competition with alien plant species, and a risk of extinction from naturally occurring events and reduced reproductive vigor due to the small number of existing individuals. The Pa-hole Gulch population on Oahu is potentially threatened by trampling and fire from military activities, and the Maui population is potentially threatened by goats and cattle. Listing of C. agrimonioides protects both varieties.

Collecting for scientific or horticultural purposes and visits by individuals avid to see rare plants are potential threats to this endangered species, whose populations are well known and near trails or roads.

Strawberry guava, a major invader of forests in the Waianae and Koolau mountains of Oahu, poses an immediate threat to two populations of C. agrimonioides. Christmasberry, now a major component of the mesic forests of the Waianae and Koolau mountains, threatens two-thirds of the C. agrimonioides populations there. Silk oak, molasses grass, and Hilo grass are serious threats to one population of the species in the Waianae Mountains, and the largest population of C. agrimonioides on Oahu is threatened by prickly Florida blackberry, as well as other invasive exotics.

On Oahu, unintentionally ignited fires have resulted from military training exercises at U.S. Army's Makua Military Reservation and Schofield Barracks Military Reservation and pose a possible threat to populations of C. agrimonioides that grow in dry and mesic forest on those lands. Accidentally or maliciously set fires in residential areas near the Lualualei Naval Magazine and the Makua Military Reservation on Oahu could easily spread and threaten one of four nearby populations of C. agrimonioides.

Conservation and Recovery

Management actions to protect endangered species, prevent range fires, and minimize soil erosion may enhance conservation of the C. agrimonioides var. agrimonioides plants found on the Makua Military Reservation. In addition, the army has constructed a fence around the population at Kahanahaiki Valley and removed all pigs from within the enclosure.

A long-range management plan for Honouliuli Preserve has been drafted. It includes actions for alien plant management, ungulate control, fire control, rare species recovery, and native habitat restoration. It is expected that these actions will benefit C. agrimonioides var. agrimonioides within the preserve.

C. agrimonioides var. agrimonioides has been successfully propagated at the Lyon Arboretum's micropropagation laboratory, at the Waimea Arboretum, and at the Division of Forests and Wildlife's Pahole Plant Nursery. Outplanting has not been attempted.

Coordinated fire protection is needed for endangered plant species on state Natural Area Reserves like Pahole on Oahu, where fewer than five individuals of C. agrimonioides var. agrimonioides remain.

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

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

Reference

U. S. Fish and Wildlife Service. 10 October 1996. "Determination of Endangered or Threatened Status for Fourteen Plant Taxa from the Hawaiian Islands." Federal Register 61 (198): 53108-53124.