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Pediocactus knowltonii
(Knowlton cactus)

[taxon report][distribution map][all photos][line drawing]



Family: Cactaceae

Scientific Name: Pediocactus knowltonii L. Benson

Synonyms: Pediocactus bradyi L. Benson var. knowltonii Backeberg [comb. illeg.]

Vernacular Name: Knowlton cactus

R-E-D Code: 3-3-3

Description: Stems 1.0-2.5 cm in diameter, solitary or a few in a cluster, barely protruding above ground level; tubercles not grooved; spines about 20 per areole, all radials, radiating from areole and appressed to the plant, 1-2 mm long, usually whitish, pinkish, or brownish and darkest at tip; flowers 1.5-2.5 cm across, fragrant, borne from previous years areoles near apex of plant, tepals white to magenta, usually pink, stigmata yellowish or pale green, ovary with few tiny papery scales; fruit barrel-shaped, fleshy, not juicy, dehiscing by circumscissile split at top and one or more vertical splits; seeds dark gray, 1.5-2.0 mm long, teardrop-shaped with low nearly flat tubercles, hilum sublateral and with a whitish strophiole. Flowers April and May.

Similar Species: Could be confused with some species of Escobaria, but it differs in having no groove on tubercles, ovary and fruit with scales, fruit dehiscent, and seeds larger and not pitted. Closely related to P. simpsonii, but it is separable by recurved appressed radial spines with no central spines; some juveniles of P. simpsonii lack central spines and are nearly identical. Other similar species occur in Arizona and Utah, but not in New Mexico.


Distribution: New Mexico, San Juan County, near the Los Pinos River.

Habitat: On rolling, gravelly hills in a piņon-juniper-sagebrush community at about 1,900 m (6,200-6,300 ft).

Remarks: This species is known only from the type locality. Pediocactus is a small genus of only seven species. Only P. simpsonii is wide ranging and common; the other six are narrow endemics with five of them, P. bradyi, P. despainii, P. knowltonii, P. peeblesianus var. peeblesianus, and P. sileri included on the Federal endangered species list.

Various sources include Colorado in the distribution of this species, largely because the type locality is very near the NM/CO border. But, no documenting specimens from Colorado exist. The Bureau of Land Management recently constructed a new fence on the true NM/CO border about 40 m north of the old fence. In 2008, Bob Sivinski who has monitored plants at the type locality for many years, did a thorough survey on both sides of the fence and concluded P. knowltonii does not occur in Colorado.

Conservation Considerations: This species was heavily collected after its initial discovery and is still popular in the cactus trade. It occurs in an area of intensive oil and gas development, but its distribution is so restricted (about 10 ha) that adverse impacts can be avoided. The type locality is healthy and reproducing; it is now privately owned and managed as a Nature Conservancy preserve. Efforts are underway to establish two introduced populations, but success is uncertain due to the slow growth of the plants.

Important Literature (*Illustration):

Benson, L. 1960. A new Pediocactus. Cactus and Succulent Journal (U.S.) 32(6):193.

*Benson, L. 1961. A revision and amplification of Pediocactus, I. Cactus and Succulent Journal (U.S.) 33:49-54.

Benson, L. 1962. A revision and amplification of Pediocactus, II-IV. Cactus and Succulent Journal (US) 34:17-19, 57-61, 163-168.

*Benson, L. 1982. The cacti of the United States and Canada. Stanford University Press, Stanford, California.

*Heil, K., B. Armstrong and D. Schleser. 1981. A review of the genus Pediocactus. Cactus and Succulent Journal (U.S.) 53:17-39.

*New Mexico Native Plants Protection Advisory Committee. 1984. A handbook of rare and endemic plants of New Mexico. University of New Mexico Press, Albuquerque.

*U.S. Fish and Wildlife Service. 1985. Knowlton cactus (Pediocactus knowltonii) recovery plan. U.S. Fish and Wildlife Service, New Mexico Ecological Services Field Office, Albuquerque.

Information Compiled By: Charlie McDonald, David J. Ferguson, 1999, last updated 2008

Agency Status:
Taxon USFWS State of NM USFS BLM Navajo Nation Natural Heritage NM Global Rank
Pediocactus knowltoniiEE.E.S1G1


Photo credits in header Peniocereus greggii var. greggii © T. Todsen,
Lepidospartum burgessii © M. Howard, Argemone pleiacantha ssp. pinnatisecta © R. Sivinski
©2005 New Mexico Rare Plant Technical Council