Opuntia arenaria (Dune pricklypear, sand pricklypear, sandbur cactus)

Opuntia arenaria (Dune pricklypear, sand pricklypear, sandbur cactus)

Photograph by Phil Tonne (2000)
Family
CACTACEAE
Scientific Name with Author
Opuntia arenaria Engelmann
Synonyms
OPUNTIA POLYACANTHA HAWORTH VAR. ARENARIA (ENGELMANN) PARFITT
Common Name
Dune pricklypear, sand pricklypear, sandbur cactus
Rare Plant Conservation Scorecard Summary
Overall Conservation Status Documented Threats Actions Needed
UNDER CONSERVED

Urban and agricultural development, Herbivory, Disease

Status surveys on abundance, distribution and threats. Collections in Socorro Co. Establish conservation area. Seed banking.


Description
Stem consisting of loosely attached flattened joints up to 8 cm in length by 2-3 cm in width, the joints highly varied in size and shape, bearing areoles with dense clumps of yellowish glochids; rhizomes and often larger roots also often bearing glochids; spines in areoles on stems slender and barbed, up to about 1.5 or exceptionally 2.5 cm long, about 3-10 per areole; spines on ovary and fruit smaller; flowers about 3-6 cm across, yellow, sometimes fading to orange; stigmas green; fruit drying to tan, rigid-walled, brittle; seeds deep brown to nearly black, invested in a hard bony off-white aril, irregular in shape, discoid with a prominent rim, roughly 5-7 mm in diameter. Flowers in May to June.
Similar Species
Opuntia arenaria is the only pricklypear with dry fruits and glochids on the roots. East of El Paso in New Mexico and Texas, O. arenaria may intergrade with O. trichophora, a species with long slender hair-like spines. Opuntia trichophora generally favors rocky, gypy, or occasionally silty habitats.
Distribution
New Mexico, southern Dona Ana, Luna, and Socorro counties; adjacent Texas, El Paso County; Mexico, Chihuahua, south to near Samalayuca.
Habitat
Sandy areas, particularly semi-stabilized sand dunes among open Chihuahuan desert scrub, often with honey mesquite and a sparse cover of grasses; 1,160-1,300 m (3,800-4,300 ft).
Remarks
This species is closely akin to other dry-fruited species of Opuntia, but due to its different and low chromosome number and morphological stability, it is usually considered to be a distinct and well defined species. Opuntia polyacantha (incl. O. erinacea) may be separated by its larger size (joints usually well over 3 cm in diameter) and firmly attached joints, as well as the fact that many individuals have pink, red, or magenta pigmentation in their flowers. Opuntia polyacantha is tetraploid (2n = 44), while O. arenaria is diploid (2n = 22). Opuntia polyacantha and O. arenaria are not known to occur sympatrically. It is often disliked by cattlemen and hikers due to its habit of loosing joints that easily attach themselves to fur and clothing. The occurrences in Socorro County need to be confirmed with collected specimens because this species is easily misidentified unless the glochids on the roots are observed.
Conservation Considerations
Much of its former habitat has been lost to urbanization and agricultural development in the Rio Grande Valley. Long-term population trends outside of the Rio Grande Valley are unknown.
Important Literature

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

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

*Benson, L. 1970. The cactaceae. In: C.L. Lundell and collaborators. Flora of Texas 2:221-317. Texas Research Foundation, Renner.

*Weniger, D. 1970. Cacti of the Southwest. University of Texas Press, Austin.

Schulz, E.D. and R. Runyon. 1930. Texas cacti. Texas Academy of Science, San Antonio.

Information Compiled By
David J. Ferguson 1998

For distribution maps and more information, visit Natural Heritage New Mexico