Aristida chaseae

No Common Name

Description

Aristida chaseae is a perennial grass with densely tufted, wide-spreading culms which may reach 20-24 in (50-60 cm) in length. The leaf blades are invo-lute, 0.08-0.12 in (2-3 mm) wide and 0.4-0.6 in (10-15 mm) long. The panicles are narrow and may be 0.4-0.55 in (10-14 mm) in length. The glumes are equal, 0.4-0.5 in (10-13 mm) long and acuminate or awn-tipped. The lemma is approximately 0.47 in (12 mm) long, narrowed at the summit but scarcely beaked and scaberlous on the upper half. The callus is 0.04 in (1 mm) long and densely pilose. The awns are equal, somewhat divergent, flat at the base, not contorted—except with age—and approximately 0.8 in (2 cm) long.

Habitat

Both of the species' population sites are located within the subtropical dry forest life zone. During 1980-93, average annual precipitation at the Cabo Rojo National Wildlife Refuge was 35 in (883 mm). The drier period extends from December through March and the wetter period includes May and September through November. Soils of the refuge belong to the Americus-Guayabo-Sosa association, and are described as well-drained to excessively drained, level to sloping, and sandy. The refuge is located at an elevation of approximately 65 ft (20 m). Vegetation is primarily grassland, but scattered individuals of mesquite (Prosopis pallida ) and aroma (Acacia farnesiana ) are found.

The species grows in exposed rock crevices and is found associated with A. portoricensis (pelos del diablo, another endangered species), Digitaria eggersii, Comocladia dodonea (carrasco), Plumeria alba (alhéli), Bursera simaruba (almácigo), Bucida buceras (ucar), Randia aculeata (tintillo), Croton sp., and Jacquinia berterii. The Puerto Rican nightjar (Caprimulgus noctitherus ), an endangered bird, has recently been reported from the slopes of the Sierra Bermeja.

Distribution

A. chaseae is endemic to Puerto Rico and was known at the end of the twentieth century from only two sites in the southwestern portion of the island: the Cabo Rojo National Wildlife Refuge and the upper slopes of the Sierra Bermeja in the municipalities of Cabo Rojo and Lajas.

A. chaseae was discovered by Agnes Chase near Boquerón in 1913. It was known only from the type collection for many years, until it was discovered by Paul McKenzie in 1987 on the Cabo Rojo National Wildlife Refuge. This new population, which contains 150-175 plants, is approximately 5 mi (8 km) to the south of the type locality. The species apparently has been eliminated from the type location, possibly as a result of competition from vigorous, introduced grass species.

In 1987, McKenzie and Dr. George Proctor located a third population on the rocky, exposed upper slopes of Cerro Mariquita in the Sierra Bermeja, a range of hills also found within the municipality of Cabo Rojo. This range of hills is the oldest geologic formation in Puerto Rico and is known for its high plant endemism. Additional localities on ridges to the west within the Sierra Bermeja were found in 1988. In these hills, it occurs at elevations of 500-1,000 ft (150-300 m).

Threats

A. chaseae historically may have extended throughout the sandy coastal areas and rocky hillsides of southwestern Puerto Rico; competition from introduced grass species, however, might have eliminated Aristida from this area, and perhaps other sites. In the Sierra Bermeja the population occurs on privately owned land that is currently subject to intense pressure for residential and tourist development. The Sierra Bermeja has been included in a proposed copper and gold mining project. Clearing of land for grazing by cattle and goats has destroyed some habitat that may have been occupied by this species. Fire in this dry southwestern range of hills is common, particularly during the drier months. Another threat stems from the occur-rence of A. chaseae within and along a roadway on Cabo Rojo National Wildlife Refuge. Because the species is known from only two localities, the risk of extinction is extremely high.

Conservation and Recovery

This species receives special protection in that it is located in the Cabo Rojo National Wildlife Refuge.

Contacts

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
1875 Century Blvd., Suite 200
Atlanta, Georgia 30345
http://southeast.fws.gov/

U. S. Fish and Wildlife Service
Boquerón Ecological Services Field Office
P. O. Box 491
Boquerón, Puerto Rico 00622-0491
Telephone: (787) 851-7297
Fax: (787) 851-7440

Reference

U. S. Fish and Wildlife Service. 27 April 1993. "De-termination of Endangered Status for Three Puerto Rican Plants." Federal Register 58 (79): 25755-25758.