The saguaro is one of the world's most studied wild plant species, probably because of its charisma and ready accessibility, but also because, as a large cactus, it is decidedly different from plants more familiar to researchers. Virtually every aspect of its life and its place in cactus evolution has been minutely examined. The essays in this book bear witness to the ongoing fascination researchers find in the great cactus, as well as the plant's unusual characteristics. There is simply no other plant like it in the United States, so instantly identifiable, so predictably located, and possessor of such a variety of distinct characteristics. It also has a national park dedicated to it, joining only the Joshua tree, the coastal redwood and the sequoia in that honor. The vast literature concerning the saguaro is testimony to its prominence as a symbol, to the perceptions it inspires, its role in human society, and its role in desert ecology.

The saguaro, with its great size and characteristic shape—its arms stretching heavenward, its silhouette often resembling a human—has become the emblem of the Sonoran Desert of southwestern Arizona. This is rightly so, for it is by far the largest and tallest cactus in the United States and our tallest desert plant as well. In this volume, we present a summary of current information about this, the desert's most noteworthy plant.

Saguaros occasionally reach 12 meters (40 feet) in height, and individuals over 15 meters (50 feet) tall appear from time to time. The record height is 23 meters (78 feet), a well-known plant of a single stalk growing near Cave Creek, Arizona, which was toppled by winds in 1986. Photos of that plant are elusive, but it was clearly a very tall cactus, perhaps the tallest of any cactus ever recorded. While other cactus species may produce individuals taller than the average saguaro, none has been documented of that stupendous height. In 1907 William Hornaday reported a saguaro between 55 and 60 feet in height. He was leader of a 1907 scientific expedition to Pinacate Volcanic Range in Mexico near the border with southwestern Arizona and was in the company of distinguished researchers. The saguaro's sole competitor for tallness in the deserts of the United States is the Joshua tree (Yucca brevifolia), a native of the Mohave Desert, a yucca that only rarely reaches 9 meters (30 feet) in height.

Saguaros are among the tallest cacti in terms of average height. They are also among those with the greatest mass. Neobuxbaumia mezcalaensis of southern Mexico, a single-stalked columnar cactus and distant relative of the saguaro, probably reaches greater average height, with individuals reaching in excess of 18 meters (60 feet). Other columnar giants include Pachycereus weberi and Mitrocereus fulviceps of southern Mexico and Pachycereus pringlei, the cardón sahueso of the Sonoran Desert in Baja California and the coastal regions and islands of central Sonora. Pachycereus pringlei and the truly massive P. weberi routinely exceed the mass of the saguaro. While columnar cacti are widespread in South America, none reaches the height or mass of the larger saguaros.