The state flower of Arizona is a mighty big deal in the Southwest, even though it is found only in a limited area.
By Lowell and Kaye Christie, F47246
Certain plants are so closely associated with particular locations that they take on a symbolic nature. The smell of pine trees brings memories of the mountains; palm trees evoke the sound of gentle waves. When you mention the desert, particularly in the Southwest, nearly everyone thinks of the saguaro cactus (Carnegiea gigantea).
The saguaro (pronounced “sah-wah-roh”) is the symbol of our favorite desert, the Sonoran desert of southern Arizona and of Mexico. Of the four deserts in North America (Great Basin, Mojave, Chihuahuan, and Sonoran), only the Sonoran has the right conditions of moisture and lack of frost for the giant saguaro cactus to grow.
Although an occasional saguaro can be found in the extreme southeast corner of California, you really have to go to Arizona or Mexico to see saguaro “forests,” thousands of specimens of the largest cactus in the United States. We have a special fondness for the saguaro, having spent several winters in a campground with a large saguaro directly outside our living room window. We spent countless hours enjoying the interaction of local animals with this amazing plant. We even tried to grow one of our own from seeds. You’ll soon learn why we gave up that endeavor.
A mature saguaro may grow 50 feet tall, weigh 10 tons, and live 150 to 200 years. But for such a large plant, it gets off to a very slow start. Beginning with a black seed the size of a pinhead, and assuming ideal conditions, the seedling may grow 1/4-inch in the first two years. If the seedling doesn’t die from drought or get eaten by an animal, it might reach 4 inches tall by the age of 10.
Then things speed up a bit. It can reach 3 or 4 feet tall by age 30. By the time it reaches 50 years old, it will produce its first blossoms, and it might be 10 feet tall. And by age 75, instead of a single towering column, the saguaro may begin sending out branches.
For those who haven’t had the pleasure of standing next to a saguaro, it is best described by exploring its structure. Inside the soft, pulpy flesh of the cactus are 12 to 30 vertical ribs, fused near the base. The ribs show through the smooth, waxy green skin as they extend vertically, forming a column 18 to 24 inches in diameter. Spaced along these ribs are the 2-inch-long spines that protect the cactus from hungry animals.
The shape of a saguaro varies depending upon the amount of moisture the plant has on hand. During a drought, the plant’s ribs will be quite evident. After one of the desert’s infrequent rains, the saguaro can absorb up to a ton of water through its shallow, widespread root system. As its water supply increases, the cactus expands like an accordion. During dry spells a saguaro relies on this moisture to survive. It will bloom and bear fruit even during the driest years.
Clusters of lovely white flowers, approximately 3 inches in diameter and with a bright yellow center, appear in May and June. These blossoms grow at the tip of the cactus column and, if the plant is old enough, from the tips of the side branches.
The flower opens for a single night, remaining open until about noon of the following day. Although insects and birds visit the open flowers, a major pollinator of the saguaro is the lesser long-nosed bat, which migrates north from Mexico in synchronization with the flowering of the saguaro.
The pollinated flower soon becomes a green fruit that ripens and bursts open to reveal a red interior. The fruit is enjoyed by all of the desert inhabitants, including humans. A mature saguaro may produce up to 200 pieces of fruit, each containing as many as 2,000 tiny seeds. Why so many seeds? Because only a few of them will survive. A researcher estimated that only two seeds from a mature saguaro’s yearly crop will actually become part of the next generation.
Because of the extreme environmental conditions in the desert, a saguaro seed needs special protection from the sun and from the many small animals that eat the seeds. Typically, surviving saguaros germinate under a “nurse plant,” another species that provides protection during the first years of a saguaro’s life. Often this is a palo verde tree that the saguaro eventually will outgrow and outlive.
Since the saguaro is the tallest cactus around, it’s no surprise that more than 20 species of birds of the Sonoran desert use it for nesting. But of particular interest is the gilded flicker. If you look carefully, you’ll often see a nest hole in the upper portion of a giant saguaro. It probably was excavated by a gilded flicker. They seem drawn by the ease of chipping away the soft cactus flesh to create a home. So many gilded flickers use the cactus as a nesting site that their range almost matches that of the saguaro.
After the flicker digs out its nest, the sap inside the hole hardens, creating permanent walls. A flicker uses its nest only for a single year, but it certainly doesn’t go to waste. Bird species unable to chip out their own nest holes are happy to move in when the flicker leaves. Even after the long-lived saguaro dies and disintegrates, the “flicker holes” remain scattered about the desert floor. American Indians gathered these holes (called “boots” because of their shape) to use as dippers and storage jars.
One of our favorite residents of the saguaro is the sparrow-sized elf owl. One lived in an abandoned flicker nest in “our” saguaro for several years, and she let us shine a flashlight on her while she sat at the opening each evening. We enjoyed the contrast of the smallest of our native owls living in the largest of our native cacti. No wonder we like the saguaro.