Arizona's Native Century Plants

WHEN the Spanish and other European explorers came to the New World in the sixteenth century following Columbus, they found many odd plants, both wild and cultivated. Among the most valuable to the Aztecs and other Indians of Mexico were some strange appearing plants consisting of a cluster of long, thick, spiny leaves and a tall flower stalk. They were common wild plants and were already in cultivationIntroduced from Mexico into the cooler parts of northern Europe as early as 1561, they grew more slowly than in their subtropical native home. Because of the long period of growth of leaves before they sent up a flower stalk and died, these plants became known as century plants. While it may take the greater part of a century for them to mature in a cold climate, in their original home they flower at an age of 10 to 20 years, or in some cases at only 3 to 5 years.

Century plants and related plants are known by a variety of names. The great Swedish naturalist, Carolus Linnaeus, gave them the scientific name Agave in 1748. (This word is pronounced a-gah-ve in Latin and a-gay-ve in English.) The word Agave, from the Greek, means noble, admirable, grand, or wonderful. It is quite appropriate, as these large, symmetrical plants with their enormous flower stalks are certainly remarkable. Included asagaves are the plants variously known as century plants, mescals, magueys, American aloes, lechuguillas, and amoles.

BY ELBERT L. LITTLE, JR. Formerly, Assistant Forest Ecologist, Southwest Forest and Range Experiment Station.*

The number of different species or kinds of agaves is very large, probably about 300. They are native only in America, where they range north to southern Utah and Nevada and south through Mexico and Central America to the upper Andes of South America. East and west their limits are the oceans. They extend through the chain of West Indian islands but not to islands far from the continent. They are most numerous in species and individuals in the arid and semi-arid parts of the table land of Mexico, and 186 species were listed in an account of agaves of Mexico.

Agaves are found at wide variations in ele vations, from sea level to 8,000 to 10,000 feet, or from areas of tropical vegetation to pine-fir forests. Most are distributed at intermediate altitudes in desert and woodland zones.

Only about 20 species are native as far north as the United States, and these are confined to six southwestern States and Florida.

Although Arizona is famous for its desert cacti. it is not well known that Arizona hasmore different kinds of native agaves or century plants than any other state in this country. Besides the large century plants, agaves include the related plants variously known as magueys, mescals, lechuguillas, and amoles.

The greatest variety of century plants in Arizona is found in the southern part of the state, and 7 species are represented within the Coronado National Forest near the Mexican. boundary. One or more species may be found at the proper elevation in most parts of the state except the northeastern quarter, however. Three or four of Arizona's species do not occur outside the state.

Because of the thick water-storing leaves, century plants are classed as succulents. While, like cacti, they have water storing tissue and formidable spines, century plants are not related to cacti. The green part of a cactus, such as a giant cactus or saguaro, prickly pear, or cholla, is the stem, and the leaves of cacti are very small, absent, or reduced to spines.

Other plants with long, evergreen leaves are less easily distinguished from century plants without examination of technical characters of flowers used by botanists. Yucca (including soapweed, Spanish bayonets, and Joshua trees), sotols, and sacahuistas or "beargrasses" are placed in the lily family, while agaves belong to the amaryllis family. All of the above plants in the lily family continue to live and grow after flowering, whereas agaves blossom but once and then die. Most yuccas and sotols have a definite trunk.

Agaves can be distinguished from all other southwestern plants by the following combination of characteristics: (1) the plant consists of a cluster of leaves spreading out from a central stem or "core" on the ground; (2) there is no trunk (in our species); (3) the usually long, stiff, thick, succulent, evergreen leaves end in sharp spines and have spines or threads along the margins; and (4) after several years of growth and food storage the plant produces a very tall flower stalk and dies as soon as the seeds mature. This last characteristic is unusual among plants.

There are two main groups of agaves, one containing mainly large plants with widely spreading branches on the flower stalks and the other group of mostly smaller plants with unbranched flower stalks. In separating the many kinds botanists use the flower structure and the size, shape, spines, and margin of the leaves.

In their native home century plants live usually from 10 to 20 years, or in some cases probably only 3 to 5 years. Size and age at flowering probably vary greatly, depending upon a number of unknown factors, including weather conditions, which affect growth, food manufacture, and food storage.

Any one can obtain data on rate of growth of century plant by marking the leaves at the top next to the bud and then counting at a later time the new leaves which have opened during the interval. Or, the date of each new leaf can even be written by scratching or cutting the surface with a knife or pencil. A few plants have been observed to form 10 to 15 leaves in one year. On experimental plots with Palmer's agave established by the Southwestern Forest and Range Experiment Station in southern Arizona, a number of plants of various sizes have been marked, so that average rate of growth can be determined.

Very young plants have small, tender, juicy leaves and are similar in different species. New leaves are formed inside the central bud, which is composed of tightly overlapping immature leaves and rests on top of the very short stem

"AGAVE" IS FROM THE LATIN MEANING "NOBLE, GRAND, ADMIRABLE." ONCE AN AGAVE PLANT SENDS UP A FLOWER STALK IT DIES. THERE ARE ELEVEN NATIVE SPECIES OF AGAVE PLANTS IN ARIZONA.