Saguaro Cactus

Introduction

Towering over the desert floor, the majestic saguaro, scientific name Carnegiea gigantea (syn. Cereus giganteus), is the largest cactus in the United States, achieving heights of up to 50 feet and weights of 6 to 8 tons. It is found only in the lower elevations of the Sonoran Desert of Arizona, California, and Sonora Mexico. It grows on flat areas and hillsides, enjoying gently sloping bajadas best. It is protected by state law in Arizona, and permits are required to move them.

Life Cycle

Once the little black seed germinates, a saguaro starts out as a small seedling, doing best if its hidden safely beneath a bush or a tree, usually a palo verde, mesquite, ironwood or creosote bush. These protective plants are referred to as 'nurse plants.' It grows extremely slowly, taking almost ten years to reach a height of one inch, 15 years to reach one foot, and forty years to reach 10 feet. Saguaros continue growing for over 100 years and live to approximately 200 years of age. The 'arms' of the saguaro start to appear at about age 75.

Flowers and Fruit

At about age 40, the saguaro will begin to produce flowers. The milky white blooms with golden yellow centers each open only once, and only at night. The flowers appear mainly at the tops of the center column and arms, but may also appear along the upper sides of the plant. A saguaro can produce hundreds of these flowers during the months of May and June. The saguaro blossom is the state flower of Arizona. The bright red juicy fruit ripens in June and July. The fruit is eaten by insects, birds, bats and animals. The Tohono O'odham Indians collect the fruit to make a ceremonial wine, often using the wooden ribs of dead saguaros to knock the fruit off the plant. Jellies, syrups and candies are also produced from the saguaro fruit.

Adaptation

The saguaro is uniquely adapted to the harsh conditions of the desert. It is composed of a single column supported by woody ribs with thick waxy skin and sharp spines running along the length of each rib. The ribs expand and contract like an accordion to accommodate the absorption and loss of water over time. The root system is very shallow but can cover a large area, enabling it to take in a great deal of water when it rains.

Saguaro as Habitat

The saguaros provide food and shelter for many desert denizens. Gila woodpeckers and gilded flickers carves out holes in the saguaro in which to lay its eggs. The cactus covers the wound with a resin-like substance, which hardens and forms something like a permanent scab on the surface of the hole. These hardened holes have the shape of boots, and that's what they are called. Once the flickers or woodpeckers leave, they don't re-use the same nest, but other birds do, such as owls, finches, cactus wrens and purple martins. Even after a dead saguaro  has fallen and wasted away, the hard boots remain along with the ribs, providing shelter for lizards and other small animals. Hawks will sometimes build their nests among the arms of the saguaro.

The Future

Some botanists believe the future of the saguaro is in serious jeopardy. The saguaro habitat has been threatened and in some places eliminated as a result of over-development, livestock grazing, wildfires, and cactus rustlers (people who remove cactus to sell or plant elsewhere.) Grazing has been restricted and halted in some areas, allowing saguaros to re-establish themselves, and wildfire management is improving. Although there are laws and penalties against cactus rustling, the practice is on the increase. One bright spot is climate change: saguaros seem to be 'climbing' to higher elevations with somewhat cooler temperatures as the lower desert gets ever hotter and drier.

Resources

Saguaro National Park
Saguaro National Park
3693 South Old Spanish Trail
Tucson, Arizona 85730

Sonoran Way
Desert USA
One World Journeys
Arizona-Sonora Desert Museum