   Appreciate the Cactuses - November 18, 1998 Jeff Schalau, County Director, Agent, Agriculture & Natural Resources Arizona Cooperative Extension, Yavapai County Though there is one genus (Rhipsalis) found in Africa and Ceylon, cactus are otherwise a New World phenomenon. In the Americas, native cactus are found from as far north as Alberta and Ontario, as far east as Massachusetts, and as far southward to include nearly all of South America. In Arizona, we are blessed with an flourishing diversity of cactuses ("cacti" is no longer the preferred term). Tourists flock to Arizona to visit the saguaros, organ pipes and barrels. In fact, there are sixty-eight species, including many varieties of each, within our state. Since most residents curse rather than celebrate cactus, it's about time they are given credit for their tenacity and ecological significance. Don=t confuse cactus with other succulent desert denizens such as yucca, agave, ocotillo or sotol. These are not cactuses even though they use some similar survival strategies. True cactuses are distinguished by their large, usually leafless stems and spines developed in clusters within spirally arranged areoles (restricted areas) on the stem. Cactus also have botanically unique flowers; the many characteristics of which the reader will be spared. Why are cactus so successful within their native range? The answer is: adaptation, adaptation, adaptation. Aside from having spines and waxy coatings to prevent moisture loss, they have developed a unique way of conducting photosynthesis: the conversion of light energy into chemical energy. All plants utilize carbon dioxide as a carbon source in the production of simple sugars (chemical energy). Most plants collect carbon dioxide for photosynthesis by opening stomata (small openings in the green portion of the plant) during the day. While these plants are collecting carbon dioxide, they are also losing large amounts of water through the stomata. This works quite well in environments that are not severely limited by water. Cactuses, as well as some other succulent plants, collect carbon dioxide by opening their stomata at night. The carbon dioxide is stored in intermediate chemical compounds until daylight comes and light energy can be utilized during photosynthesis. This strategy greatly reduces water loss during the day and allows these plants to survive in extremely arid environments. With all their adaptations, cactus are by no means immune to predation. Insects, diseases, and large animals have found way to utilize these plants for their own benefit. I find two of these quite interesting. The first is the Cochineal scale: an insect that lives on prickly pear cactus and is treasured for its red pigment that is widely used as a dye in cosmetics, fabrics and food. Look for this whitish insect and squeeze it with your hand. You'll be amazed at the brilliance of the color. The second is the javelina. These animal utilize prickly pear for a significant portion of their diet and eat pads and fruit including a healthy dose of spines. Actually, many animals, including humans, eat the sweet fruit of this cactus. Contact the University of Arizona Cooperative Extension office for recipes for nopales (tender prickly pear pads) or prickly pear jelly. If you've lived in Arizona long enough, you probably have a good cactus story. My favorite involves our dog, Rusty, a red chow-mix and a detached section of teddy bear cholla. Rusty was a curious puppy exploring the Sonoran desert near Tucson for the first time when he discovered the piece of cactus on the ground. It stuck to his nose. My wife and I laughed as Rusty instinctively shook his head thereby sending the spiny projectile hurtling toward my lower body. I was lucky that there was a triple layer of denim at the point of impact and no permanent damage was done, but the story also illustrates the propensity for cholla to expand it's range. Each piece that hitches a ride on an animal (humans included) will likely take root and start a new plant and potentially a new colony. This is just another handy adaptation of the cactuses. By the way, a pocket comb is indispensable for removing stray pieces of cholla. The University of Arizona Cooperative Extension has publications and information on plant science and horticulture. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 or E-mail us at mgardener@kachina.net and be sure to include your address and phone number. |