Endangered Species Recovery Program
Like other beavertail cacti (Opuntia species), Bakersfield cactus is a perennial with fleshy, flattened, green stems (pads). The pads of Bakersfield cactus vary in outline from rounded, heart-shaped, or diamond-shaped to nearly cylindrical. A single plant may consist of hundreds of pads, which originate both at ground level and from the tips of other pads. The number of individuals in a population may be difficult to determine because pads from adjacent plants often overlap. Thus cactus populations are described by the number of clusters (groups of pads that are rooted at the same point) rather than as a number of individuals.
The pads and fruits are dotted with eye-spots, which are rounded structures that contain barbed bristles. Tiny leaves are produced on the youngest pads of beavertail cacti, but are quickly shed. The flowers of the Bakersfield cactus are magenta. The dry fruits are the size and shape of small eggs and may contain grayish-white seeds.
Few details on the life history of Bakersfield Cactus are available. The fleshy stems, tiny, short-lived leaves, shallow root systems, and specialized physiology common to most members of the cactus family are adaptations to growth in arid environments. Known to typically flower in May, the reproductive biology of this taxon has not been studied. Certain other Opuntia species require cross-pollination for seed-set and many are pollinated by bees. Vegetative reproduction, which is the production of new plants from sources other than seed, is typical in Bakersfield cactus and several related species. Fallen pads easily root if sufficient water is available, but Bakersfield cactus does not survive prolonged inundation. Bakersfield cactus produces seeds infrequently. Cactus seeds require warm, wet conditions to germinate, a combination which is extremely rare in the Bakersfield area. Pads may be dispersed by flood waters, but seed dispersal agents are unknown.
Soils supporting Bakersfield cactus typically are sandy, although gravel, cobbles, or boulders also may be present. Known populations occur on flood plains, ridges, bluffs, and rolling hills. The Bakersfield cactus is a characteristic species of the Sierra-Tehachapi Saltbush Scrub plant community, but populations near Caliente are in Blue Oak Woodland and the Cottonwood Creek population is in riparian woodland. Many sites for Bakersfield cactus support a dense growth of red brome and other annual grasses. Sand Ridge is characterized by sparse vegetation and a preponderance of native species such as California filago (Filago californica) and yellow pincushion (Chaenactis glabriuscula). Historical records indicate that the majority of Bakersfield cactus occurred at elevations ranging from 140 to 260 m (460 to 850 ft). The highest-elevation population is at 550 m (1,800 ft) near Caliente and the lowest is at 121 m (396 ft) at Fuller Acres.
The Bakersfield cactus is endemic to a limited area of central Kern County in the vicinity of Bakersfield. The California Department of Fish and Game considered the pre-1987 reports to represent approximately 33 occurrences. However, based on written descriptions, historical photographs, topography, and deductions from plant morphology, the populations most likely were more or less continuous. As of 1987, the northern, southern, eastern, and western limits of the known range, respectively, were Granite Station, Comanche Point, Caliente, and Oildale.
Approximately one-third of the historical occurrences of the Bakersfield cactus have been extirpated, and the remaining populations are highly fragmented. However, the known range was extended to the south when several occurrences were discovered in the late 1980's in south-central Kern County, just north of Wheeler Ridge. The extant occurrences may be grouped into the following areas of concentration: 1) Caliente Creek drainage (Caliente-Bena Hills), 2) Comanche Point, 3) Cottonwood Creek, 4) Fairfax Road-Highway 178-highway 184-Kern Bluffs-Hart Park, 5) Fuller Acres, 6) Granite Station, 7) mouth of Kern Canyon, 8) Oildale-Kern River Oil Field-Round Mountain Road (separated from area #4 by the Kern River), 9) Poso Creek, 10) Sand Ridge, and 11) Wheeler Ridge-Pleito Hills.
The primary reason for the decline of the Bakersfield cactus was habitat loss. The formerly extensive tracts of Bakersfield cactus near Edison and Lamont were destroyed by conversion to row crops and citrus groves; much of the conversion occurred prior to 1931. Residential development, petroleum production, sand and gravel mining, and off-road vehicle activity also have contributed to habitat loss and fragmentation of this plant and continue to threaten the existing populations. Other threats include competition from introduced grasses, air pollution, and low genetic diversity.
Order CARYOPHYLLALES, Family CACTACEAE, Genus Opuntia, Species basilaris
The taxonomy of the Bakersfield cactus has not been universally accepted with some experts considering it to be a full species. In the most recent treatment, the scientific name of the Bakersfield cactus is given as Opuntia basilaris var. treleasei. (var. represents variety; in plants a variety is equivalent to a subspecies in animals.) Opuntia basilaris var. kernii is the other recognized variety.
Opuntia treleasii (type specimen)
Calif. Dept. Fish and Game. 1995. California Diversity Database. Sacramento, Electronic form; Parfitt, B.D., and M.A. Baker. 1993. Opuntia. Pp. 452-456, in The Jepson manual: higher plants of California (J.C. Hickman, ed.). Univ. California Press, Berkeley, 1400 pp; Benson, L.D. 1982. The cacti of the United State and Canada. Stanford Univ. Press, Stanford, CA, 1044 pp; Twisselman, E.C. 1967. A flora of Kern County, California. Univ. San Francisco, San Francisco, CA, 395 pp; Munz, P.A., and D.D. Keck. 1959. A California flora. Univ. California Press, Berkeley, 1681 pp.
up to 35 cm (14 inches) high and 10 m (33 ft) across
up to 5mm (0.2 inches)
less than 7 mm (0.3 inches)
Bakersfield cactus is unique among the varieties of O. basilaris in that the eye-spots contain spines in addition to the bristles. Other features of Bakersfield cactus that differentiate it from related beavertail cacti include the smooth pad surfaces, cylindrical pad bases, non-sunken eye-spots, and longer (up to 5 mm [0.2 inches]) leaves. The two varieties of O. basilaris differ from each other in that variety treleasei has spines less than 7 mm (0.3 inches) long (which may be longer or shorter than the associated bristles) and eye-spots even with the pad surface, whereas variety kernii has spines longer than 7 mm (0.3 inches) and raised eyespots.
N. L. Brown and E. A. Cypher