15 December 2012
World's Largest Collection of Opuntia (Cactaceae), prickly pear cacti
I'm re-posting excerpts and you can read the entire fascinating article at Outcome Magazine
" Last June, as Eric Ribbens and I perused his collection of his Opuntia fragilis — probably the largest collection of its kind on the planet — located near the Western Illinois University School of Agriculture’s Farm in Macomb, the Department of Biological Sciences Professor and Fulbright Scholar told me about the unusual sex life of this rare and endangered prickly pear cactus.
“If you’re going to go through the work of having sex, the goal is to maximize the genetic recombination. Yet, in plants, it’s possible for pollen to move to the same plant. But for the Opuntia fragilis, these plants have some sort of a chemical recognition cue, and if they sense the pollen is from themselves, they shut it off and they won’t let it fertilize the egg. We don’t know exactly what is going on, but it turns out, in Illinois, at least — and I suspect throughout the rest of the Midwest, although we haven’t studied it yet — it doesn’t really matter if we take pollen from your flower or we take pollen from a flower nearby or pollen from a flower from a quarter-mile away, they all get shut off. So, somehow, the plant’s mechanism is saying, ‘All of this pollen is from me.’ Or that pollen is a mechanism that’s broken and not working right. We don’t really know what is going on.”
Based on his extensive research of the Opuntia fragilis species, Ribbens has provided strong evidence this species, in the Midwest at least, has forgotten how to have sex. It still tries now and then, though, he added with a smile.
“About 10 years ago, I applied for and received a grant from the Illinois Endangered Species Protection Board to study Opuntia fragilis at the Lost Mounds site, a decommissioned munitions depot with a large Opuntia fragilis population covering about 100 acres,” Ribbens explained. “The grant provided funding for a graduate student research assistantship to investigate the population status and fungal infections. So, my grad student, Barbara Anderson, and I designed a project to determine turnover in pad production and to study flowering in this species of prickly pear cactus.
Considering its aversion to reproduction, one wonders how the Opuntia fragilis — which is sometimes referred to as the “brittle” variety — continues on? Ribbens asserts the fragility of its pads — hence, part of its eponymous scientific name, fragilis, and common name, “brittle” prickly pear—provides its survival mechanism.
The Making of a Midwestern Cactus Mission
For many, the thought of cactus plants can conjure desert scenes in drier, arid landscapes. But the Opuntia fragilis, which Ribbens began studying by accident, likes a chillier climate.
“This particular species grows on rocky outcrops, and it likes it when it’s cold. It is a small, northern species of cactus, growing almost as far north as the Arctic Circle. Although it is widely distributed across North America, in the upper Midwest it is rarer, and in Michigan it is a state endangered species,” he noted. “I got started studying Opuntia fragilis at my first teaching position at St. John’s University in Stearns County Minnesota. An undergrad student there found them growing. He thought it was a new discovery, but it turned out that a lot of people had known about it already. Still, it caught my attention.” According to Ribbens, at the time, he was looking for a plant species to try to study a particularly difficult problem in spatial plant ecology.
In spite of that, Ribbens continued his pursuit of the prickly pear.
“One of the fun things about it is it’s rare and endangered enough that people are somewhat interested in it, and there is a little bit of grant money out there for research possibilities. But it’s common enough that it’s not like I’m going to accidentally wipe it out,” he explained. “After I received tenure at WIU, I applied for a sabbatical, and for that, I proposed to attempt to locate every population of Opuntia fragilis in five Midwestern states. I searched herbarium records, contacted state natural resource departments or agencies, talked to cactus enthusiasts around these states and built a list of sites where we knew Opuntia fragilis had, at one point, grown. Some of those sites were gone and others certainly still existed, but for many, the status was uncertain.”
Ribbens said during two summer seasons he and crews of WIU students traveled around the Midwest searching for Opuntia fragilis sites. He said they were able to investigate all but four sites they had pinpointed.
Ribbens’ research and interest in Opuntia fragilis also garnered international interest, when, several years ago, he was contacted by the editor of a Polish cactus journal, Kaktusy.
Ribbens’ large prickly pear cactus collection near the WIU School of Ag’s University Farm indeed illustrates his dedication to learning about the plant. He not only has Opuntia fragilis specimens from all the sites he traveled to and investigated — as well as specimens from South Dakota, North Dakota, Colorado, Oregon and from Canada — he has also collected specimens of two larger species of prickly pears that grow in the Midwest.
Patterns and Pollination Plans
Over the next few years, Ribbens has specific plans to continue his prickly pear cactus research and collaborative relationships. In 2009, he traveled to Utah with a WIU undergraduate student Bill Schmidt (senior, biology, Mokena, IL) and met with cactus enthusiasts there, who showed him populations of Opuntia fragilis around the state, and in particular, locations where it seemed to be hybridizing with several other species of Opuntia fragilis.
“This was partially funded by a grant from the Cactus and Succulent Society of America. I have data, photographs and live specimens from that trip, and I am working on an analysis that I hope to publish,” he said.
Ribbens said this year has been an exciting one for his Opuntia fragilis plants, as it is the first one during which they produced flowers. Next year, he plans to try some pollination experiments among different populations to further explore what might be preventing Midwestern plants from producing seed. He also would like to locate five or six additional possible sites in Iowa for the bigger species and write, with Majure, an analysis of the Iowa-growing Opuntia humifusa and Opuntia macrorhiza.
While Ribbens admits he doesn’t necessarily enjoy providing the answer to the inevitable question about the subject of his work — “Just what are the Opuntia fragilis good for?” — he remains undaunted in his pursuit of knowledge about this rare plant.
Read the entire article at the link above.