Siler Pincushion Cactus

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Siler Pincushion Cactus

Pediocactus sileri

ListedOctober 26, 1979
FamilyCactaceae (Cactus)
DescriptionSpherical cactus with yellowish flowers.
HabitatClay soils rich in gypsum and calcium.
ThreatsOff-road vehicles; collectors; uranium mining.
RangeArizona, Utah


Siler pincushion cactus (Pediocactus sileri ) is formed of inconspicuous globular stems, solitary or clustered, up to 4 in (10.2 cm) in diameter. Each spine cluster (areole) contains between three and seven straight or slightly curved central spines about 1 in (2.5 cm) long. These central spines are dark brown and lighten to nearly white with age. Each areole also has 11-16 whitish radial spines, which are slightly shorter than the central spines. Yellowish flowers with maroon veins, about 1 in (2.5 cm) in diameter, appear in spring. Fruits are greenish-yellow and dry out at maturity.

Siler pincushion cactus has also been classified as Echinocactus sileri and Utahia sileri. This species was originally labeled endangered, not threatened, when it was first listed by the U. S. Fish and Wildlife Service (FWS) in 1979. In December 1993 it was reclassified under the threatened status because of the ongoing success of recovery efforts.


Siler pincushion cactus is found on gypsum-and calcium-rich soils derived from the Menkopi formation. These soils are high in soluble salts that, while inimical to many plants, apparently suit this cactus, which does not grow well in other soils. The rolling clay hills where Siler pincushion cactus grows have a barren "badlands" appearance. Elevations are from 2,000-5,400 ft (610-1,646 m). At higher elevations, trees and small shrubs become more abundant.


Restricted to a highly specific soil type, Siler pincushion cactus probably never extended much beyond its current range in northwestern Arizona and southwestern Utah.

Siler pincushion cactus is sparsely distributed in a narrow band that extends from southeast of Fredonia (Coconino County) west for about 70 mi (113 km) into north-central Mohave County, Arizona. This range is only about 30 mi (48 km) wide and reaches north, extending slightly into Utah's Washington and Kane Counties. The total population was estimated at about 7,000 individual plants when surveyed in the mid-1980s.


Siler pincushion cactus was listed as endangered in 1979 because of threats posed by livestock grazing, off-road vehicles, mining, road construction, and illegal collecting. Recovery actions carried out in the 1980s and early 1990s by the Bureau of Land Management included developing a habitat management plan and conducting surveys for other populations. As a result, the status of Siler pincushion has improved, although it is not yet secure enough to remove from protection under the Endangered Species Act. In recognition of the progress made toward full recovery, the FWS reclassified Siler pincushion on December 27, 1993, to the less critical category of threatened.

Gypsum mining in the area was considered a major threat to this cactus when it was first listed. Potential uranium mining, however, now seems a greater danger. By 1990 much of the "Arizona Strip" had been claimed by uranium mining companies, and more than 200 mining plans had been filed 81 within the cactus's habitat. A rise in uranium prices could induce mining companies to develop these claims.

Portions of the habitat have been overgrazed by livestock, contributing to erosion of the slopes. Off-road vehicle disturbance has also increased, particularly near towns. The sparse, rolling hills are attractive sites for off-road recreation, but the vehicles create erosion channels that are destructive to the habitat.

Conservation and Recovery

Cactus collectors pose a continual threat. From 1982 to 1984 Siler pincushion cacti were offered for sale in five plant catalogs, one even specifying "field-collected plants." Attempts are currently under way to develop techniques for nursery propagation of the cactus to supply the commercial trade.

Siler pincushion cactus is listed as a protected plant in Arizona, which prohibits collecting except by permit. It is considered a species of concern by the Convention on International Trade in Endangered Species (CITES). The success of ongoing recovery efforts has conservationists hopeful that Siler pincushion cactus might someday be delisted.


U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
P. O. Box 1306
Albuquerque, New Mexico 87103-1306
Telephone: (505) 248-6911
Fax: (505) 248-6915

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


Gierisch, R. K. 1981. "Observations and Comments on Pediocactus sileri in Arizona and Utah." Desert Plants 3: 9-16.

U. S. Fish and Wildlife Service. 1986. "Siler Pincushion 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.