Arizona-Sonora Desert Museum Digital Library

Agaves are among the most conspicuous plants of arid North America; their bold forms attract attention in any landscape whether natural or designed. All are characterized by succulent or semisucculent leaves that form rosettes from a few inches to several feet across, but there are many variations on this basic pattern. Most species are essentially stemless but a few grow trunks that creep along the ground. Some species have only one rosette; most multiply by underground suckers and may develop into large colonies. Agave leaves vary from green through bluish to silver-gray, and are often strikingly banded with different shades of color. Leaves range from long and narrow to short and broad, and from arrow-straight to gracefully recurved or haphazardly twisted. The leaf margins are typically lined with large, sharp spines (teeth) and each leaf is usually tipped with a hard, sharp spine. A few species have leathery, unarmed leaves. The leaves are so tightly compacted in the growing tip that the teeth leave imprints on both surfaces of adjacent leaves after they unfurl, overlaying their own complex patterns over the banding. These imposing features make agaves popular among succulent collectors and landscape designers.

Various agave species have also been and continue to be important sources of food, fences, rope, medicine, and liquor. The Mescalero Apaches were named for their dependence on this plant. Before them the Hohokam cultivated agaves as a major food crop (see A. murpheyi).

Agaves flower on tall, branched or unbranched stalks that grow from the center of the leaf rosette. As a plant approaches maturity at 10 to 30 years of age it accumulates a great quantity of sugar and starch in the heart tissue. These carbohydrates provide the energy that fuels the rapid development of the inflorescence (the flowering structure, including supporting stems), which is usually massive compared to the plant that produces it. In all but a few species the rosette dies after flowering and fruiting, having spent all of its life energy to produce a huge quantity of seeds — a monocarpic (once-fruiting) life cycle. The plants literally flower themselves to death.

Though the flowering rosette usually dies, many species produce vegetative offsets (suckers or pups in English, hijos or "sons" in Spanish) before or after flowering. In this way clones (multiple, genetically identical, individuals that originated from a single original seed) form colonies that may persist for centuries or longer.

Range

The genus ranges from Utah in western North America through Mexico (where the most species are found), with a few in northern South America and on Caribbean Islands. The majority of agave species occur in semiarid habitats above the desert, especially in desert grasslands and oak-pine woodlands. About 40 of the 150 North American species occur in the Sonoran Desert region.

Ecology

Agaves typically grow on well-drained, rocky slopes. Different species are adapted for pollination by insects, nectar-eating bats, and hummingbirds. Seeds are dispersed by wind, usually only a short distance from the parent.

The two major groups, or subgenera, of agaves are distinguished from each other by whether their inflorescences are obviously branched or not. Most species in the subgenus Agave (branched inflorescences) developed features that enable them to be pollinated by nectar-feeding bats, although other pollinators may currently be more important. They grow whitish to yellow flowers which produce copious nectar and pollen at night. Bats are attracted by the fragrant nectar, which usually smells unpleasant to humans — like ammonia or rotting fruit, depending on the species. Agave nectar and pollen are major food sources on the northernmost and southward legs of the bats' migratory routes. After wintering in the Mexican tropics, bats migrate northward through the desert following the south-to-north wave of spring-blooming columnar cacti. They raise their young in southern Arizona, then return south via the mountains, feeding on agaves. Hawk-moths are also common visitors to the night-flowering agaves and are probably effective pollinators; bees and other diurnal insects aid in pollination as well.

Some species in the subgenus Agave occur outside the range of the bats, or flower at a season when the bats are not present. These have colored diurnal flowers that are pollinated by hummingbirds and bees. Species in the subgenus Littaea (which bear unbranched spikes) are pollinated mainly by insects and sometimes hummingbirds.

Of the 40 or more agaves in our region, several are ecologically or horticulturally important. Agave americana, a very large plant with rosettes up to 12 feet (3.7 m) broad, is by far the most commonly used in gardens in the southwest U.S. and worldwide, although most of its natural range is outside the Sonoran Desert region. In our species accounts, we focus on some of the more interesting local species.

Ethnobotany

Several beverages are made from the sugar-rich juices of mature agaves. The extracted juice is drunk fresh as aguamiel (honey-water) or fermented into pulque; both are popular beverages south of the Sonoran Desert. Steamed heads or central stalks are mashed and allowed to ferment with added liquid. After several days, the resulting fluid is distilled into the potent liquor mescal. The most widely known local ("bootleg") variety of mescal is Bacanora, named after that Sonoran town and made from Agave angustifolia. Other varieties of bootleg mescal are made in nearly every Mexican village within agave habitat. Tequila, the most famous legal variety of mescal, is made from the single species Agave tequilana, grown near the town Tequila in Jalisco. Tequila is to mescal much as Chardonnay is to wine.

Mature agaves also provide food. The leaves are cut off near their bases, leaving a cabeza ("head") resembling a giant pineapple, weighing up to 70 pounds (32 kg). The cabezas are usually pit-roasted in large numbers and eaten during fiestas. (Note: The raw flesh of many agaves is caustic and can even blister skin.)

Behind the formidable appearance of agaves and the plants formerly grouped with them is a wealth of uses. They have long been and still are used extensively by indigenous peoples throughout North and Central America for food, fiber, and medicine. The roasted, sugar-rich agave hearts have been an important food for numerous Native American groups. Juice from the mature plants is consumed both fresh and fermented. Fermented liquid from the cooked heads is distilled into mescal. Tequila, the best-known variety of mescal, is distilled from one species, Agave tequilana. The tequila agave (mezcal azul) is a significant economic crop in southern Mexico; North Americans alone consume more than a million gallons of tequila a year.

Fiber from the leaves of Agave sisalana is the source of sisal rope, and A. fourcroydes yields henequen fiber. Sisal is a major economic product widely cultivated in Africa, Asia, as well as in the New World; it provides 70 percent of the world's hard, long fiber for ropes, rugs, and bags in recent decades. Numerous native American peoples weave baskets from the fibers of yuccas and nolinas.

The complex chemicals in this family have many uses. Compresses for wounds have been made from macerated agave pulp, and juices from leaves and roots were used in tonics. But beware — sap from many agaves can cause severe dermatitis. The juice of the more virulent agaves has been used as fish poison and arrow poison. Agaves and yuccas are used in Mexico to make soap. Yuccas were once used to provide the foam of root beer and are still used in livestock deodorant. More recently steroid drugs have been synthesized from extracts of several species in the family.

Today these plants are appreciated for their beauty and are widely used to add accents to landscape designs and mark property boundaries all over the world. Howard S. Gentry's book Agaves of Continental North America was so popular that it was reprinted in 1992, an unusual event for a botanical monograph.

As originally described by Gentry, Agavaceae consists of 18 genera and a little over 400 species, many of them native to western North America. This family is difficult to define; it has been revised by taxonomists several times in recent years.

Agaves, yuccas, and relatives were once included in the very large lily family Liliaceae. Gentry segregated agaves, yuccas, and other genera into their own family Agavaceae in the 1970s. More recently other botanists have split the old Liliaceae into many more families and removed some genera from Agavaceae, among them Nolina, Dasylirion, Sansevieria, and Dracaena. Whatever their taxonomic status, these are highly useful plants with dramatic forms.