The saguaro cactus is one of the defining plants of the Sonoran Desert here in Arizona. These plants are large, tree-like columnar cacti that develop branches (or arms) as they age, although some never grow arms. These arms generally bend upward and can number over 25. Saguaros are covered with protective spines, white flowers in the late spring, and grow red fruit in summer.
PLEATS – Saguaros have pleats that allow them to expand when they drink water (like an accordion) and contract as they use up their water supply. Each pleat hosts a row of spine clusters. Each spine cluster can grow multiple buds, flowers, fruit, and maybe grow into an arm. One theory behind why some Saguaro become “Crested” is that the control mechanism the determines the amount of pleats is out of control. So instead of occasionally branching, there are multiple branches created the crests.
How Saguaros Reproduce
In late April through early June, the tops of the saguaro’s trunk and arms sprout a profusion of large, creamy white flowers. Individual flowers open at night and close the following afternoon. To develop into fruits, they must be pollinated within this time frame. Pollination is carried out by nectar feeding bats, birds and insects.
Each fruit contains about 2,000 tiny black seeds. When the fruit and seeds are eaten by a coyote or cactus wren, the seeds pass through their digestive system unharmed and are distributed throughout the desert. However, if the seeds are eaten by a dove or quail, they will be completely consumed in the digestive system. Occasionally, a dove feeding her young may inadvertently drop a seed on the ground, giving that seed a chance at life.
It is estimated that a saguaro can produce some 40 million seeds during its lifetime. However, few will survive to become a seedling. Fewer still will become an adult. The low survival rate of seedlings can be attributed to drought, prolonged freezing, or animals eating them.
Saguaro Cactus Fruit and Exposed Seeds
Saguaros are found exclusively in the Sonoran Desert. The most important factors for growth are water and temperature. If the elevation is too high, the cold weather and frost can kill the saguaro, so they are not usually found above 4,000 feet. Although the the Sonoran Desert experiences both winter and summer rains, it is thought that the Saguaro obtains most of its moisture during the summer rainy season.
With the right growing conditions, it is estimated that saguaros can live to be as much as 150-200 years old.
Saguaro are very slow growing cactus. A 10 year old plant might only be 1.5 inches tall. Saguaro can grow to be between 40-60 feet tall (12-18m). When rain is plentiful and the saguaro is fully hydrated it can weigh between 3200-4800 pounds.
The saguaro is the largest cactus in the United States.
Most of the saguaros roots are only 4-6 inches deep and radiate out as far from the plant as it is tall. There is one deep root, or tap root that extends down into the ground more than 2 feet.
After the saguaro dies its woody ribs can be used to build roofs, fences, and parts of furniture. The holes that birds nested in or “saguaro boots” can be found among the dead saguaros. Native Americans used these as water containers long before the canteen was available.
Crested Saguaro – The growing tip occasionally produces a fan-like form which is referred to as crested or cristate. Though these crested saguaros are somewhat rare, more are found each year. Biologists disagree as to why some saguaros grow in this unusual form. Some speculate that it is a genetic mutation. Others say it is the result of a lightning strike or freeze damage. At this point we simply do not know what causes this rare, crested form.