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Cyperus trachysanthos

ListedOctober 10, 1996
FamilyCyperaceae (Sedge)
DescriptionPerennial grasslike plant.
HabitatWet sitesmudflats, wet clay soil, or wet cliff seepson coastal cliffs or talus slopes.
ThreatsLow numbers; competition with alien plants; fire; off-road vehicles; potentially by pumping of the wetland for flood and mosquito control; modifications to the wetland topography; mowing; herbicide application; Hawaii Army National Guard activities such as the cleaning of vehicles, dumping of paints or thinners, or the use of pesticides; goats, cattle, and deer predation; collectors.


Cyperus trachysanthos (Pu'uka'a), a member of the sedge family (Cyperaceae), is a perennial grasslike plant with a short rhizome (underground stem). The densely tufted culms (aerial stems) are sticky, obtusely triangular, 8-18 in (20-46 cm) in height, and leafy at the base. The linear leaf blades are green, covered with a waxy coating, and somewhat leathery. The leaf sheath is yellowish-brown and partitioned with nodes. The flower clusters are 2-3.5 in (5-9 cm) long and 2-5 in (5-12.5 cm) wide. Each flower head contains 10-30 pale yellowish-brown spikelets, each of which contains eight to 20 flowers. The glumes (small pairs of bracts at the base of each spikelet) are broadly egg-shaped. The fruit is a dark brown, egg-shaped achene. This species is distinguished from others in the genus by the short rhizome, the leaf sheath with partitions at the nodes, the shape of the glumes, and the length of the culms.

First collected between 1816 and 1817 in the "Sandwich Islands" (the former name of the Hawaiian Islands), C. trachysanthos was described by William J. Hooker and G. A. W. Arnott in 1832. This species has been maintained in the most recent treatment of Hawaiian members of the genus. The specific epithet refers to the rough or papery flowers.


C. trachysanthos is usually found in wet sites mudflats, wet clay soil, or wet cliff seepson coastal cliffs or talus slopes at elevations of 10-525 ft (3-160 m). Plant associates on Kauai include Hibiscus tiliaceus (hau), Plantago lanceolata (narrow-leaved plan-tain), and Pteris vittata.


Historically C. trachysanthos was known from Niihau, Kauai, scattered locations on Oahu, Mauna Loa on Molokai, and Kaena on Lanai. This species is currently known from eight populations on Niihau, Kauai, and Oahu that harbored a total of at least 517 individuals in 1997. On privately owned Niihau, an unknown number of individuals were known from an area west of Mokouia Valley. More than 300 individuals were known on Kauai from state land in the Nualolo Valley. On Oahu, five plants occurred at Kaena Point Natural Area Reserve, 110 in and around Manini Gulch, 38 from state land at Diamond Head, 37-39 at Makapuu, three at Queen's Beach, and about 24 individuals at the Kawainui Marsh area.


Statewide, C. trachysanthos faces the potential risk of stochastic extinction from naturally occurring events due to its small number of occurrences and modest total population; on Oahu, the species is threatened by competition with alien plants, fire, and off-road vehicles. The population in Diamond Head may also potentially be threatened by the pumping of the wetland for flood and mosquito control, modifications to the wetland topography, mowing and herbicide application, and runoff from nearby Hawaii Army National Guard activities such as the cleaning of vehicles, the dumping of paints or thinners, and the use of pesticides.

Goats are contributing on Kauai to the decline of one population of C. trachysanthos. Cattle, deer, and goat predation is a possible threat for this plant since it is not known to be unpalatable to these animals.

Collecting for scientific or horticultural purposes and visits by individuals avid to see rare plants are potential threats to C. trachysanthos.

On Oahu, C. trachysanthos is threatened by alien grasses and possibly by koa haole. The largest population of C. trachysanthos, in the Nualolo Valley on Kauai, is threatened by established alien species, Plantago lanceolata (narrow-leaved plantain) and Pteris vittata.

Conservation and Recovery

In 1995 the Hawaii Army National Guard funded the U. S. Fish and Wildlife Service to conduct endangered species surveys of its lands throughout the state and to make recommendations for management of endangered species on these lands, including C. trachysanthos. Management recommendations for the endangered C. trachysanthos in Diamond Head included weed control, deterrents to vehicle access, modification of mowing and herbicide application regimes, modification of water pumping regime, a documented protocol for contaminant spill cleanup, cultivated propagation, and enhancement of the existing population. The State of Hawaii has constructed barriers to off-road vehicle traffic in Kaena Point Natural Area Reserve, which may protect the population there.

C. trachysanthos has been successfully cultivated at the National Tropical Botanical Garden, where more than 3,000 seeds were in storage in 1997.

Once adequate propagated material is available and weed control is underway in the areas of the remaining natural populations, enhancement of the remaining wild populations by outplanting should occur. Establishment of new populations within the historic range of the species should be initiated in areas free from the impacts of alien plants.


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. 10 October 1996. "Determination of Endangered or Threatened Status for 14 Plant Taxa from the Hawaiian Islands." Federal Register 61 (198): 53108-53124.