English Names: many-headed barrel, cottontop cactus
Scientific Name: Echinocactus polycephalus
Spanish Names: biznaga, biznaga de chilitos
View all images of Echinocactus polycephalus
This Echinocactus is unique as the only barrel in our region that branches under normal conditions. The 8-inch (20 cm) diameter heads occur in clusters of up to 200, forming mounds to 3 feet (1 m) across and somewhat less high. The dense, stout spines obscure the plant bodies and restrict the small yellow flowers from opening fully; they appear in July. The brown spines appear bright red when wet from rain.
This cactus occurs mostly on rocky and gravelly slopes in the driest parts of the Sonoran and Mohave deserts. It is rarely found where rainfall exceeds 5 inches (130 mm). (E. polycephalus var. xeranthemoides, occurs in the northern Mohave and Great Basin deserts, where there is more rain.)
Many-headed barrel cacti are slow-growing and probably very long-lived. Plants grown from seed at the Desert Museum are just beginning to branch at nearly 20 years of age. This species is also geographically stable; its range has not changed for at least the past 30,000 years despite the dramatic climatic swing from ice age to a warm interglacial period. Though the fruits seem to be imprisoned within the spiny armor, birds and packrats can get to them and disperse the seeds.
Turk's head or eagle's claw cactus (E. horizonthalonius var. nicholii) is in the same genus but has a different growth habit; it nearly always has a single stem. One variety of Turk's head is common and widespread in the Chihuahuan Desert. Our variety is endangered and restricted to 3 small populations in Arizona and Sonora on limestone. The flowers are pollinated by bees. The fruits remain buried among the spines; they eventually disintegrate and the seeds simply fall to the base of the mother plant. Bighorn sheep and javelina eat the whole plants and probably function as occasional long-distance seed dispersers. Javelina only recently migrated into the Sonoran Desert, and their added predation may be exterminating this cactus.
The stems are globular to columnar, usually unbranched, and pleated, ranging from less than a foot (30 cm) tall in the smallest species to 6 to 12 feet (1.8-3.7 m). The central spines are the larger of two types and arise from the center of the areole; the principle central spine often has a different shape from that of all the other spines. Radial spines are smaller and arise from the margins of the areoles. The short, funnel-shaped flowers are very stiff and usually don't extend beyond the spiny armor. The thick rind of the fruit is dry at maturity in most Echinocactus. The seeds are packed in a dry interior, not embedded in pulp. Echinocactus differs from Ferocactus in having sharp-pointed scales on the flower tubes and woolly ovaries.
There are 6 species of Echinocactus in the world. In the Sonoran Desert there are two species.
The surface area of barrels and other more or less globose plants is small compared to the volume, so evaporative losses are small relative to the large volume of water stored. Repeat photography of sites in Baja California in 1905 and the 1990s indicate that the life spans of barrel cacti are typically less than a century.
One of the great fables of desert survival is that barrels and other cacti are reservoirs of water that can be easily tapped and drunk. It is true that indigenous peoples and a few other desert residents know how to obtain emergency water from cacti. But most city dwellers, including most aspiring survivalists, could not get water from any cactus if their lives depended on it (pun intended).
The first problem is getting to the pulp inside the very tough and spiny epidermis. A pocket knife is inadequate, and tools that are typically carried in a car, such as tire irons, aren't very effective either. The labor of cutting into a barrel on a hot day is likely to cause loss of more water from sweating (and perhaps bleeding) than one would gain from the cactus.
Secondly, the water in cactus pulp is tightly bound in a gooey mucilage. Most of the year the pulp is more like a damp sponge than a watermelon — you can't squeeze much liquid out of it. Furthermore, the raw pulp of many cacti is inedible. Some species have potentially toxic levels of oxalic acid (prickly pears), bitter and sometimes toxic alkaloids (senita and many other cacti), or other substances that cause diarrhea (some barrels) or vomiting. The best cactus for emergency water is Ferocactus wislizeni. See more details under that species. For a historical account of extracting water from a barrel cactus (in cool weather and when it was legal), see Camp-Fires on Desert and Lava by William T. Hornaday, pages 216-219.
Water can be obtained from cacti using a machete and solar still. But anyone with the foresight to pack these tools is smart enough to carry plenty of water and inform friends of the itinerary and expected return date!
Caution: native wild cacti are protected by state laws; it is illegal to take or destroy them. In addition, most barrels cannot branch, so cutting out the top is lethal.
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.