Saguaro Cactus of the Sonoran Desert

Slow-growing saguaro is a symbol of the desert

As a visitor to the southwestern United States a couple of weeks every year, I had always won­dered about the saguaro cactus that signals a wel­come to the vast Sonoran Desert.
Like stoic sentinels standing guard, the giant saguaro marches up mountains, occupies highway roadsides and even lives along golf courses.
No two are alike. They inhabit only the Sonoran Desert, an area that includes parts of Arizona, Cal­ifornia and Mexico.
Many are simply green spiny trunks rising out of the shadows of a paloverde tree or a bursage bush. Others have arms that reach up to the sky and may be 30 feet tall.
They don’t bloom until they are about 50 years old. The mature giant finally gets an appendage around its 75th birthday. The strange plant may tower in the desert until it is 200 years old and sport multiple branches.
Fascinated, I ventured out to the Desert Botani­cal Garden in Phoenix, where the silhouetted saguaro grows prolifically.
Nancy White, the assistant director of education at the Desert Botanical Garden, talked about the saguaro’s role in the desert’s ecology.
Nature has finely engineered the saguaro, which can weigh several tons, and can survive extreme temperature fluctuations.
“Think of a Hummer vehicle loaded with the family and the dog,” White said.
The columnar structure of the pleated accor­dion- like surface allows the saguaro to expand or contract depending on the amount of water it’s storing. It holds so much water that it can go for many months without rain.
The saguaro is able to withstand storms and winds that blow across the desert thanks to sys­tem of lateral roots that run just below the ground’s surface. As soon as it rains, these roots and other hair-like roots suck up as much mois­ture as they can. Often, these roots twine around rocks and give the saguaro a phenomenal struc­tural strength.
In late May, the saguaro sprouts creamy white blossoms with yellow centers that cluster near the ends of the branches. The blossoms open during cooler desert nights and close again by next mid­day.
Not all of the flowers in a single saguaro bloom at the same time. Instead, over a month or more, a few open each night, secreting nectar into their tubes and awaiting pollination. These flowers close at about noon the following day, never to open again.
Bats and moths feed on the nectar, pollinating the plant to produce a pink fruit about the size of a kiwi that has bright scarlet pulp with tiny black seeds. The fruit, said to be one of the tastiest foods of the desert, ripens just before the fall rainy sea­son. It is hard to pick one before the birds and other insects get to it.
The native people harvest the fruit with a long tool made from the dead skeletal wood of the saguaro. They make preserves and syrups from the delicacy.
Fruit left on the tree drops its seeds. They ger­minate and start growing under a nurse plant. In about 10 years, the new saguaro will be about the size of a thumb. Eventually, the nurse plant may die as the saguaro takes its water. To survive, the saguaro seed needs the shade and protection of a nurse plant, such as a paloverde or bursage.
The typical mature saguaro is a happy hotel for the birds that inhabit the Sonoran Desert. The gila woodpecker drills holes in the saguaros. That’s just fine with the saguaro as it forms a “scab” that becomes a nesting house.
The nests maintain a comfortable temperature even during the warmest summer days because of protection from the sun and the natural air condi­tioning provided by the saguaro.
Many varieties of birds live in nests in the saguaro, including the woodpecker, cactus wren, elf owl, screech owl, sparrow hawk and white­winged doves.