Arizona-Sonora Desert Museum Digital Library

Description

The Sonoran Desert species of this genus have upright stems, usually not more than a foot (30 cm) tall, and typically in clusters. A few of the 44 currently recognized species in the genus have single stems. The ribbed stems help distinguish hedgehogs from the mammillarias, with which they are sometimes confused. Spines are straight or slightly curved, never hooked as in many mammillarias. The flowers are funnel-shaped or partly funnel-shaped, but abruptly flaring outward about 2½ inches (6 cm) across in most Sonoran Desert species. Some are long, narrow funnels conducive to hummingbird or moth pollination. Flowers come in many colors, including white, yellow, pink, purple, and red; some are bicolored. The stigmas are usually green. Some species of Echinocereus are readily distinguished from other cacti by the flower buds that rupture through the skin of the stem, rather than emerging from the areoles. Nearly all species flower in the spring, though a Baja California species flowers in August or September. One species within the Sonoran Desert and a few beyond it have thin, trailing stems.

Range

Species occur in nearly all habitats in the arid southwestern United States and southward well into Mexico.

Notes

The fruits of several species are large, juicy, and tasty. They were eaten by indigenous peoples when they could get them before the birds and squirrels did. The genus is popular among cactus collectors because most species are of moderate size and have beautiful flowers.

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.

Range

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.

Notes

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.