Davis' Green Pitaya

Echinocereus viridiflorus var. davisii

Description

Davis' green pitaya, Echinocereus viridiflorus var. davisii, is a dwarf cactus, usually growing as a single stem with six to nine ribs. The stem is turbinate to ovate, up to 1 in (2.5 cm) tall and 0.8 in (2 cm) in diameter. Each spine cluster (areole) consists of eight to 11 radial spines, which are white, gray, or gray tipped with red. Typically, each cluster has a single prominent central spine but the number may vary.

Plants mature after three or four years and bloom in late March and early April. The yellow-green flowers are nearly as large as the plant itself. The stubby, green fruit ripens in May. A metallic green sweat bee (Family Halictidae) is believed to be the major pollinator. The bulk of the stem is often underground and can be hidden by other low-growing plants, such as little club moss. Some scientists have referred to this species asE. davisii.]

Habitat

Davis' green pitaya grows in semi-arid grasslands of the Chihuahuan Desert, an area that receives 16 in (41 cm) annual precipitation. It is restricted to rock crevices along ridgetops composed of outcroppings of the Caballos Novaculite formation. The habitat supports perennial bunch grasses and a wide variety of shrubs and cacti at an elevation of 3,960-4,455 ft (1,200-1,350 m).

Distribution

This cactus is endemic to Brewster County in the Big Bend region of Texas.

A single population of Davis' green pitaya is known from near the town of Marathon in northern Brewster County. This population totaled about 20,000 plants in 1984, a significant increase over previous counts. It is believed this increase was due to favorable weather conditions in 1983.

Threats

Twenty years ago, the green pitaya had nearly been collected to extinction by European, Japanese, and American collectors. Today it is threatened by multiple pressures: collection by both commercial and private collectors, competition for space and moisture, and highway fence construction and maintenance. The destruction and modification of the habitat by overgrazing of livestock, brush control, and herbicide use also impact this species.

Conservation and Recovery

The population site, with the cooperation of the private landowners, has now been securely fenced, which seems to have stopped bulk collecting. Annual monitoring indicates that the number of cacti has stabilized and may be climbing. The cactus has recently reestablished itself at several sites where it had previously been eliminated.

All of the population occurs on private land, and the posting of "No Trespassing" signs discourages collectors. The landowners have also been cooperating to reduce disruption of habitat.

The Recovery Plan recommends studying: the feasibility of reducing collecting by promoting a nursery propagation program, the plant's seed dispersal methods and seedling establishment, and the pollinators.

Contact

Regional Office of Endangered Species
U.S. Fish and Wildlife Service
P.O. Box 1306
Albuquerque, New Mexico 87103
http://southwest.fws.gov/

References

Benson, L. 1982. The Cacti of the United States and Canada. Stanford University Press, Stanford.

U.S. Fish and Wildlife Service. 1984. "Davis' Green Pitaya Cactus Recovery Plan." U.S. Fish and Wildlife Service, Albuquerque.

U.S. Fish and Wildlife Service. 1987. "Endangered and Threatened Species of Texas and Oklahoma (with 1988 Addendum)." U.S. Fish and Wildlife Service, Albuquerque.