English Name: Engelmann prickly pear, tuna
Synonyms: Opuntia phaeacantha discata
Spanish Name: nopal, abrojo, joconostle, vela de coyote
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Opuntia engelmannii [Opuntia phaeacantha discata]
Engelmann prickly pear is a shrubby cactus forming hemispherical mounds up to 5 feet (1.5 m) high and two or three times as wide. Pad size varies with individual plants; the largest are over a foot (30 cm) long. (these giants may be hybrids with other species.) The spines are also variable. The O'odham recognize this variability in applying four or five names to different forms. The flowers are yellow, about 3 inches (8 cm) in diameter, and bloom in May near the end of the spring flowering season. They last a day each, and those of some plants age to orange by afternoon. The juicy fruit ripens to varying shades (from plant to plant) of rich purple to red. The specific status of this plant is still in dispute; it has been shuttled between Opuntia phaeacantha, O. discata, and O. engelmannii by different taxonomists during the past few decades.
Opuntia engelmannii [Opuntia phaeacantha discata] and Opuntia phaeacantha var. major hybridize freely with each other and sometimes with other species, so it is often difficult to identify a particular plant.
Opuntia engelmannii [Opuntia phaeacantha discata] and Opuntia phaeacantha var. major are the most common prickly pears over much of the arid Southwest from inland Southern California to central Texas and south into northern Baja California and central Sonora.
Engelmann and several other species of common, large prickly pears present an ecological mystery. The juicy, palatable fruits ripen in tremendous numbers in July and August. Most saguaro fruits, produced in similar abundance earlier in the summer, are devoured the same day they ripen. But Engelmann prickly pear fruits persist for several months. Though they are eaten by a wide variety of animals including rabbits, packrats, javelina, deer, squirrels, numerous birds, desert tortoises, and cactus beetles, there are far too many fruits for them to consume. Moreover, the fruits in the centers of large plants are out of reach of several of the wildlife species that would eat them; many of these fruits are still present in November fermenting and shriveling. Why would a plant seemingly waste energy in such overproduction? Could there be a vacant niche, a missing seed-disperser? The large, very hard seeds offer another possible clue. It has been suggested that some prickly pears coevolved with the now-extinct giant mammals, such as mammoths and ground sloths. It's an intriguing theory and, if proven true, further illustrates the already-established fact that natural systems are anything but static.
Genus Opuntia (incl. Cylindropuntia, Grusonia, and Corynopuntia)
The genus Opuntia is quite large, yet it is still replete with hidden diversity. The more closely botanists study these plants the more species they discover. People who live with and use these plants recognize even more differences between them than do botanists. Juanita Ahil was a Tohono O'odham who lived in the desert near Sells, Arizona. Ecologist Tony Burgess could recognize two species of opuntia growing in Juanita's yard. Juanita was able to distinguished five different kinds from the appearance of the prickly pear pads alone. Later, the characteristics of the fruits these plants produced confirmed that she was correct; the fruits differed accordingly in color, taste, and keeping qualities.
Opuntia has been the main genus in the Opuntioid subfamily of Cactaceae. (A new classification system for this group is underway; see below. Until this revision, all of the other cacti in the Sonoran Desert region are in the Cereoid subfamily.) The Opuntioid are distinguished from other cacti by four characteristics. First, the stems grow in distinctly jointed segments. The elongation of joints is permanently terminated by the onset of the dry season; subsequent growth of the plant occurs by the initiation of new joints by branching from the areoles. (Other cacti have indeterminate growth. A saguaro stem, for example, grows ever longer each growing season until the plant dies or the stem tip is damaged.) Second, whether or not they have regular spines, Opuntioid areoles bear glochids (usually small to minute, barbed spines that are very sharp and brittle, and very easily detached). Third, rudimentary leaves are present on new joints. Fourth, the seeds have a pale covering called an aril; most other cacti have shiny black seeds. The largest genus, Opuntia, has at least 300 species of shrubby or arborescent plants worldwide. The vernacular names are based on growth form. The chollas (most of our species are in the subgenus Cylindropuntia) have cylindrical stem segments, while those of prickly pears (subgenus Platyopuntia) are flattened.
The genus ranges from southern Canada to southern South America, in habitats ranging from arid desert to tropical semiarid woodlands and high mountains.
In general, chollas are more drought tolerant than prickly pears and extend into drier deserts. Less arid habitats tend to have more prickly pear species. All desert species are pollinated by a few species of bees that specialize in cacti; they collect the pollen to feed developing larvae. Some opuntia flowers emit a fragrance of damp earth; perhaps the smell resembles “home” to the ground-nesting bees. Mature fruit ranges from tan or green and dry to bright red or purple with juicy pulp; all contain large, very hard seeds. Many birds, mammals, and insects feed on the fleshy fruits; so may desert tortoises and spiny iguanas. Though all species flower, some rarely, if ever, produce viable seeds; these species reproduce almost entirely by vegetative means.
Both prickly pears and chollas provide shelter for numerous animals. White-throated wood rats (packrats) build nests of sticks and other debris within the shrubby prickly pears. (The shrubby ones are those with thickets of pads on the ground, as opposed to the trunked species, such as santa-rita prickly pear). Packrats cover their houses with a layer of cholla joints, if available. In more exposed locations the nest may consist almost entirely of piled-up cholla joints. These nests provide good protection from coyotes, but not from snakes, which can enter the nests along the trails used by packrats. (Rattlesnakes commonly take up residence in packrat nests, usually after eating or evicting the packrat.) Cactus wrens prefer to build their nests among the stems of chollas. Curve-billed thrashers, mourning doves, roadrunners, and other birds also commonly use both chollas and prickly pears as fairly secure nesting and roosting sites.
The flesh of prickly pears and some chollas is eaten by jackrabbits, packrats, and javelina, all of which can deal with concentrations of oxalic acid that can be toxic to many animals and can clog the kidneys of species with highly concentrated urine. Several insects have also coevolved with cacti as their sole food source. The most conspicuous are the giant cactus beetle (Moneilema gigas), cactus weevils (Metamasmius spp.), cochineal (Dactylopius spp.), and a moth (genus Copidryas cosyra) with very colorful but rarely-seen larvae that feed on fresh cholla stems. Read about the blue cactus borer (Cactobrosis) in the saguaro section.
Opuntias are extensively used for food and other purposes by humans. The fleshy fruit (called tuna in Spanish) of some species (O. engelmannii in Arizona Upland) is edible and tasty. It can be eaten fresh, if care is taken to avoid the glochids on the rind. More often the brilliant red-purple and distinctly-flavored juice is expressed to make drinks, syrup, and jelly. Some prickly pear species are commercially cultivated for fruit production; numerous superior cultivated varieties have been selected.
The formidable flower buds of some chollas are eaten by O'odham and other desert dwelling peoples. The buds are rolled on the ground or another hard surface with sticks to remove the spines and glochids. The buds are pit-roasted for a day, and either eaten immediately or dried and pickled for later consumption. Cholla buds contain significant protein, but they are probably more important for their high calcium content and soluble fiber. The O'odham harvested and ate them early in the dry season after the last year's crops had been consumed, and before saguaro fruits ripened. Cholla buds are still part of the traditional O'odham diet. The Hohokam, predecessors to the O'odham, also ate cholla buds, and there is evidence that they cultivated chollas around their homes.
Millions of people cook and eat the tender young pads of several species of prickly pear. Besides being more tender, immature pads have less oxalic acid, which could be toxic in large amounts. Nopales (the edible species of prickly pear and the harvested whole pads of the same) are very nutritious. Nopalitos (small pads that are cut into bite-size pieces) are mucilaginous like okra, and good for thickening broths. The mucilage also helps control blood-sugar levels associated with adult-onset diabetes. Diabetes is a common affliction among native Americans who adopt Western high-fat, low-fiber diets. There is also clinical evidence that nopales reduce blood cholesterol. Widely ignored by Anglos, who often regard them as worthless nuisances, opuntias are abundant and healthy foods for those who know how to use them.
Prickly pears are a historically important reason that the Spaniards continued their conquest of the New World. They quickly looted the precious metals they were after, but they also discovered cochineal. Cochineal is a scale insect that feeds on prickly pears. Its body fluids contain a bright crimson, foul-tasting substance that protects it from predators. Ground up cochineal insects were used by native peoples to dye their textiles rich red or purple, depending on the processing. In Europe this color of dye was so rare that only royalty could afford it. In some kingdoms the colors “royal purple”(derived from a sea cucumber) and, after discovery of the New World, royal crimson from cochineal, were reserved for the king by law. The cultivation and export of cochineal dye became a major economic activity, and its source was kept secret for many years. The commercial cochineal was harvested and later cultivated from prickly pears in southern Mexico. Our Sonoran Desert species contain the same dye.
When competitors finally discovered the source of the coveted dye, they attempted to establish populations of prickly pears and cochineal in other countries such as India, Ceylon, South Africa, and Australia. In many cases the cochineal died out, but the prickly pears escaped into the wild and became serious pests.
The cochineal industry thrived until the late 1800s, when cheaper aniline dyes became available. However, there is still significant commercial cochineal production in several countries, including Mexico. Cochineal is one of a very few red dyes approved by the U.S. Food and Drug Administration. (Earlier red food colorings were found to be carcinogens and were banned.) Today red candies, beverages, and lipstick are often colored with bug blood raised on prickly pears. Despite its evolutionary origin as an anti-predator toxin, the quantities used to color foods are nontoxic to humans, except for occasional allergic reactions (which can be caused by almost any substance).
The juice expressed from prickly pears has been used for centuries to strengthen adobe mortar. It was recently used in the restoration of the San Xavier Mission in Tucson. It is being tested for similar applications, such as stabilizing dirt footpaths and erosion-prone slopes.
Recent genetic studies reveal that the different subgenera of this genus may be distinct enough to warrant their elevation to full genera. In our region there would be three new ones: Opuntia would include all Sonoran region prickly pears. Most chollas will be in Cylindropuntia, and the few club chollas will be placed in Grusonia or Corynopuntia.
Numerous species of cholla and some prickly pears hybridize with one another. Hybrid populations are fairly common. Some of these hybrids may reproduce sexually; others are sexually sterile but can reproduce vegetatively. There are several such “clonal microspecies” in the Tucson area alone, some of which are restricted to a patch of just a few acres (hectares). Most of the descriptions of these species are published only in scientific monographs and have not yet appeared in general plant lists and keys. So if you are frustrated with being unable to identify a cholla or prickly pear from a field guide, be assured that you're not alone. No field guide can cover all the possible hybrids and “microspecies.”(See also the note under Opuntia acanthocarpa.)
Opuntias have captured the imagination of botanists as reflected in some of their names. My two favorites are from Baja California. Opuntia (Grusonia) invicta roughly translates “invincible points”; its English vernacular name is devil's club cholla. This cactus forms low mounds of ovoid joints covered with broad, 3-inch (7.5 cm) long spines like little daggers. Even better is Opuntia (Cylindropuntia) molesta — no translation needed. It's a shrub sometimes over 8 feet (2.4 m) tall, and its spines are 2 inches (5 cm) long and incredibly sharp. I have mused that the botanist who named it might have discovered it in the same manner as I did. There were hundreds of 2 foot (60 cm) tall plants on a gravelly wash bed. It was a wet spring and the grass was 3 feet tall. . . .
Cactaceae (cactus family)
The enormous popularity of cacti among gardeners and plant collectors is surpassed only by that of roses and orchids. Their appeal extends far beyond their native habitat; there are legions of devotees in the eastern United States, Europe, and Japan. The desire to possess these strange yet beautiful plants supports hundreds of specialty nurseries; the largest shops grow and sell millions of plants annually. Cacti are one of the reasons tourists visit the American southwest.
Description of Family
Most people think they know a cactus when they see one, but they are often mistaken. All cacti are succulents, but not all succulents are cacti. Agaves, ocotillos, aloes, and the succulent euphorbias (such as African milk trees) are among the swollen or spiny plants often mistaken for cacti. However, the term cactus refers to a particular family of plants defined by a distinctive flower pattern. To be a cactus, the plant must produce flowers with the following characteristics: many tepals (combined sepals and petals) that intergrade with each other; many stamens (usually hundreds), and numerous stigma lobes (rarely only three). If a plant lacks such a flower, it cannot be a cactus.
The cactus family is nearly endemic to the New World from southern Canada to southern South America. There is an exception — one of the 1800 species occurs naturally in Africa, Sri Lanka, and Madagascar. However, introduced cacti have gone wild and sometimes become pests in several regions of the Old World. Cacti are most common (in numbers of both plants and species) in semiarid habitats with low rainfall, yet with dependable rainy seasons. A few species occur in extremely arid deserts and wet tropical forests. About 300 species occur in the Sonoran Desert region.
The majority of cactus species are pollinated by numerous species of bees, a number of which specialize in cacti. Cactus bees are all solitary, but in some species the females congregate by hundreds of thousands at nesting sites to dig their individual nest burrows, which are densely concentrated in an area of a few thousand square feet. Cactus pollen is packed into these burrows to feed the grubs, which the parents do not tend. Some cacti are pollinated by birds, moths, or bats.