Opuntiads of the USA

Contributed article: Eric Ribbens, PhD (June, 2009)

Opuntia fragilis (Nutt.) Haw. is a small, cold-hardy prickly pear. It has pads 1 to 2 inches long, rather round, with spines that can be longer than the pad. The plant will form a sprawling prostrate mat up to two feet in diameter; rarely are there erect chains of more than 3 or 4 pads. Flowers are large and yellow, with creamy greenish to reddish centers. Older plants often develop a rather thick root-stock at the base of the plant, and can be comprised of hundreds of pads on numerous flat chains.

The common name, fragile prickly pear, refers to the ease with which pads will break off and start new plants, which at least in the midwest is the main method of reproduction. Flowering is apparently an optional response when resources are abundant, and in many populations flowers have never been observed. Ribbens and Anderson showed that in Illinois pollen from the same flower cannot fertilize the eggs, a form of incompatibility known to occur in the Opuntia which increases genetic recombination in offspring. However, in the midwest, this reproductive strategy seems to have resulted in a nearly complete absence of seed production.

Scientifically, it has been investigated primarily to examine its cold tolerance mechanisms. Apparently in fall it becomes more tolerant to freezing, probably due to a combination of water loss and increases in abscisic acid, and it has been shown that populations located further north demonstrate higher cold tolerance than more southerly populations. There is little evidence of ethnobotanical use, although the pads apparently have been roasted and eaten as a hardship food by some Native American groups.

The range of Opuntia fragilis is centered in the northern Great Plains, where it is fairly common in the Dakotas, Alberta, and the eastern parts of Montana, Wyoming, and Colorado. Its range extends into the midwest, with an outlying population in eastern Ontario. It is scattered throughout the west, where it prefers somewhat cooler climates. A very cold-tolerant plant, it is found almost as far north as the Arctic Circle in western Canada. In the midwest, most populations are located on igneous or sandstone rock outcrops, where Opuntia fragilis inhabits narrow transitional areas where enough soil and water accumulate to support spike mosses and mosses, but not enough resources to permit competition from other vascular plants. It also grows in rather thin prairies growing on very sandy soils.

Current Research: Dr. Ribbens has been locating sites where Opuntia fragilis has been reported in five midwestern states. (The CSSJ pdfs below tell some of the stories of these hunts). We have initiated a DNA investigation in which we are analyzing DNA obtained from most of these populations. We are using ISSR markers and comparing them to microsatellite primers in an attempt to identify patterns of relationships between the various midwestern populations. Secondly, we are trying to grow live plants from pads obtained from these various populations. Currently we are comparing the growth rates of plants with and without fertilizer. If these plants grow large enough to flower, we plan a series of controlled cross-pollinations to investigate the mystery of the lack of fruit production in the midwest. Finally, in a separate project we have been compiling herbarium records, and plan to analyze the geographical distribution of Opuntia fragilis.

How can you help? Any information about where Opuntia fragilis is currently growing would be helpful. Specifically, I am looking for precise location information, ideally with a description of the population size. So "Opuntia fragilis grows in eastern Oregon" is not very helpful, but "In summer 2008, I saw a large population of Opuntia fragilis about 2 miles NW of Laramie, Wyoming" is helpful. Even more helpful would be to send me a few pads from the population. And don't think that because it's common that I don't need to hear about it ... Opuntias are generally poorly documented, especially in areas where the species is more abundant. Secondly, I'm also interested in Opuntia humifusa and Opuntia macrorhiza. Finally, I am always looking for money and for interested graduate students!

For more information about the taxonomy, appearance, geographic distribution, and ecology of Opuntia fragilis, go to the Opuntia fragilis Webpage or enjoy some of my articles on Opuntia fragilis.
Opuntia fragilis taxonomy, distribution, and ecology (Haseltonia 14:94-110, 2008),
Opuntia fragilis in Iowa (Cactus and Succulent Journal 81:9-13,40, 2009),
Opuntia fragilis in Michigan (Cactus and Succulent Journal 80:240-244, 2008), and;
Opuntia fragilis in Illinois Cactus and Succulent Journal 80:119-122, 2008).

Permission to reproduce the PDF articles is through the courtesy of the Cactus and Succulent Society.

Dr. Eric Ribbens
Biology
Western Illinois University
Macomb, IL 61455