By Tom Schweich
We have two Pricklypear or Opuntia cacti that are common in Golden open spaces and along trails. Sometimes they are right next to each other. They are the “Western Pricklypear” (Opuntia macrorhiza Engelm.) and the “Plains Pricklypear” (Opuntia polyacantha Haw.)
The flowers of the two species are very similar, but the species are easily distinguished by looking at the spines on the pads. Western Pricklypear has large white spines only on the top half of the pads, whereas Plains Pricklypear has large white spines covering the entire pad.
Western Pricklypear (Opuntia macrorhiza Engelm.) has been found on North and South Table Mountains, Dakota Ridge, Schweich Hill, the Survey Field, and
DeLong Park. In Colorado it is found along the Front Range and foothills with a few collections in the Colorado mountain valleys.
The cactus was first described by George Engelmann, M.D. (1850) from a collection by Ferdinand Lindheimer on the Guadalupe River of west Texas. Lindheimer was a member of the German colony at New Braunfels, Texas, and made thousands of plant collections in Texas in the 1830s and 1840s.
The other cactus, the Plains Pricklypear (Opuntia polyacantha Haw.) is also found in most localities in Golden, specifically North and South Table Mountain, Dakota Ridge, Schweich Hill, Deadman Gulch (Kinney Run) and the Survey Field. In Colorado there are many collections from the plains, foothills, and mountain valleys.
Plains Pricklypear was recognized as a species by Thomas Nuttall (1818) who wrote that he had seen it on the dry plains of the Missouri River in 1811. At the time, all cacti were known by Linnaeus’ (1753) generic name of Cactus. Unfortunately, Nuttall’s name of Cactus ferox had been previously used for a different cactus. Adrian Haworth (1819), after studying a specimen of Plains Pricklypear grown in the Physic Garden of Chelsea along the Thames River in London, provided a valid name of Opuntia polyacantha Haw. It was common for North American plants to be grown in the botanic gardens of England, where they were described scientifically.
There are several other Pricklypears (Opuntia spp.) that some cactus experts believe occur along the Front Range, though our current Flora of Colorado (Ackerfield, 2022) does not agree. Chief among them is “Grassland Pricklypear” (Opuntia cymochila) described by George Engelmann M.D. & J. M. Bigelow when describing the cacti from Whipple Expedition of the Pacific Railroad Surveys (1853-1855). We will have to leave the question of whether the Grassland Pricklypear occurs in Colorado to the Pricklypear experts.
