Opuntia mojavensis

Engelmann & Bigelow, Proceedings of the American Academy of Arts and Sciences 3: 293, 1856

Lectotype; Drawing (The Botany of the Expedition, 1856)

Details

Opuntia mojavensis is an enigma. The only  historical drawing shows 2 spine clusters and an immature or sterile fruit. The herbarium sheet (lectotype) also has limited material. Britton and Rose reported that the species was imperfectly understood. We observed a colony of plants growing at the summit of Mt Potosi near Las Vegas, NV that might be O. mojavensis. The spines seem similar to those of the lectotype and in the drawing above. The original location (mountains above Victorville, CA) matches the location in general terms of plant companions and altitude but is about 150 miles west of Mt. Potosi. The photographs presented here represent our concept of the species, but more study is needed. See the original description. O. mojavensis may be hexaploid.

Read more below thumbnails.


The spines from the plants on Mt. Potosi occur from the center of the pad to the tip. Areoles across the central part of the cladode often have 2 white spines that are strongly reflexed. The adaxial spine is typically much longer than the other (up to 2-inches long). Spines on upper portions of cladodes often darken to brown at the base; there may be 4(5) spines in the upper areoles. Pads are  often 6- to 9(10)- inches long and 6- to 7-inches wide, but they may be subcircular. Cladodes turn distinctly reddish in freezing temperatures. Cladodes dimple but do not wrinkle in freezing weather and they remain upright over the winter.

The upright tendency of the plants is different from the typical stance of O. phaeacantha. Another difference is that the fruit of O. mojavensis has no stipe. It is subglobular. Because of their more upright stance, differences in spination, and fruit shape, we present these plants as a distinct species. However, differences notwithstanding, it is possible that these plants are not a distinct species but are a robust variant of O. phaeacantha. Alternately, it may be that these plants represent a western population of O. dulcis.

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