Knowlton Cactus

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Knowlton Cactus

Pediocactus knowltonii

ListedOctober 26, 1979
FamilyCactaceae (Cactus)
DescriptionDwarf, globular cactus, lacking central spines; pink flowers.
HabitatNavajoan Desert; sagebrush and pinyon pine.
RangeColorado, New Mexico


The dwarf Knowlton cactus, Pediocactus knowltonii, is a nearly globular cactus with solitary or clustered gray-green stems, from 0.3-1 in (0.5-2.5 cm) tall and from 0.4-1.2 in (1-3 cm) in diameter. Spine clusters (areoles) are characterized by 18-23 radial spines with no central spines.

Most plants bloom at three or four years of age, budding in early April and flowering until early May. Pink flowers open by mid-morning, close in late afternoon, and persist two or three days. Fruits form by early June, and seeds disperse in late June, falling to the base of the parent plant. Rain then carries seeds downslope where they sprout among cobbles or at the base of other plants.


Knowlton cactus occurs within the Colorado Plateau Province of the Navajoan Desert and is found along the slopes of the San Juan Mountains.The cactus is restricted to red-brown clay soils, derived from alluvial deposits that overlie the San Jose Formation. These deposits form rolling, gravelly hills covered with pinyon pine, Rocky Mountain juniper, and sagebrush. The surface is strewn with rocks from pea to cobble-sized. Habitat elevation is between 6,800 and 7,600 ft (2,075 and 2,300 m).


This species was once more numerous in northern New Mexico and possibly extended into La Plata County, Colorado. The distribution pattern is highly localized.

The Knowlton cactus survives at a single site of about 11 acres (5 hectares) in San Juan County, New Mexico. This population was estimated to number about 100,000 plants in 1960, but by the mid-1970s, numbers had declined so steeply that many collectors thought the cactus was extinct. By 1987, the population had rebounded slightly to about 7,000 plants and by 1993 to 9,000. The cactus has been recently transplanted to two additional locations.


Systematic collecting has been the major reason for the decline of this species and continues to threaten its survival. Although the cactus's flowers are small and not showy, collectors prize it for its rarity alone. Many private and commercial collectors know the location of the Knowlton cactus population and have returned on a regular basis to take wild plants, even though greenhouse plants have recently been cultivated.

In 1960, while the nearby Navajo Dam was under construction, well-meaning members of a local cactus society set out to rescue Knowlton's cactus from an expected inundation. This group collected thousands of plants from the population and sought to transplant them, but the transplanted colonies did not survive. As it turned out, the dam reservoir never flooded the site.

In addition to collectors, several natural threats to the cactus have been identified. Many plants have been found with root systems exposed, apparently pushed completely out of the ground by frost heave, and cacti growing on the steep slopes are often undermined by erosion.

Conservation and Recovery

To help preserve the Knowlton cactus, the Public Service Company of New Mexico donated 25 acres (10.1 hectares) containing part of the surviving population to the Nature Conservancy. The organization then erected a strong barbed wire fence to keep out livestock and to deter collectors. Many seedlings have since been observed at this site, offering hope for recovery if the plants are left undisturbed.

In addition, cuttings of the cactus were transplanted to a protected site in 1985 and have shown a 93% survival rate for new seedlings. Half of the surviving plants there are flowering and fruiting. A second site was established by seed in 1987. Botanists will compare data from the two sites to determine which transplantation technique works best in preparation for expanding the reintroduction effort.


Regional Office for Endangered Species
U.S. Fish and Wildlife Service
P.O. Box 1306
Albuquerque, New Mexico 87103

Regional Office for Endangered Species
U.S. Fish and Wildlife Service
P. O. Box 25486
Denver Federal Center
Denver, Colorado 80225


Backeberg, C. 1982. The Cacti of the United States and Canada. Stanford University Press, Stanford.

Knight, P. 1981. "Rare, Threatened, Endangered, and Other Plants of Concern in the BLM Chaco-San Juan Planning Area of Northwestern New Mexico." New Mexico Department of Natural Resources Heritage Program, Santa Fe.

U.S. Fish and Wildlife Service. 1985. "Knowlton Cactus Recovery Plan." U.S. Fish and Wildlife Service, Albuquerque.

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

U.S. Fish and Wildlife Service. 1985. "Knowlton Cactus Recovery Plan." Albuquerque. 53 pp.

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Knowlton Cactus

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