Arizona has many sights that are unique, including several types of cactus that grow wild nowhere else in the world.  One of them is the Saguaro cactus.  While they grow statewide, they are best viewed in one of the many protected areas that will give you information as well as interaction.  One good choice is the Saguaro National Park near Tucson.  Here one can hike for miles, choosing guided tours, educational trails, or individual hiking.  Information is plentiful about indigenous desert plants, especially the stately Saguaro cactus.

photo by Alice Shoaf

The Saguaro cactus (Cereus giganteus) is only indigenous to the Sonoran Desert region in North America, primarily in central and southern Arizona.  It is an awesome plant with specimens reaching 50 feet high and a trunk radius up to 30 inches around.  Slow-growing, it gains an inch or two per year, and is thought to have a life span of up to 200 years.  At about 15 years old it will begin forming branches, usually around 5 on a mature plant.

photo by Alice Shoaf

Often the Saguaro grows beneath a ‘nurse plant’ like the one in the photo above.  A nurse plant is a larger bush or tree that supplies shade and moisture until the young cactus is well established.  The nurse plant will eventually die, as the thirsty cactus will hoard the water.  Hardy nurse plants, like this Ironwood tree, this can live on for years,  but you can see the tree is being affected.

photo by Alice Shoaf

The cactus flesh is waxy and supple, allowing for expansion and contraction between ribs.  Clusters of 1 to 2-inch spines grow the entire length.  The root system is surprisingly shallow, supported on a tap root that is roughly 3 feet in diameter and reaching down only about a foot.  Smaller roots stretch radially about as long as the cactus is high.  This root system allows for a massive sponging up of water when it rains, and supports the cactus through the long dry seasons.  During extended drought the Saguaro will shrink in; when it rains the meat will then plump up like an accordion.  After a hard rain, the Saguaro can gain up to a ton in water weight.

The slow growth and great capacity of the Saguaro to store water allow it to flower every year, regardless of rainfall. The night-blooming flowers, about 3 inches wide, have many creamy-white petals around a tube about 4 inches long. Like most cacti, the buds appear on the southeastern exposure of stem tips, and flowers may completely encircle stems in a good year.  These blooms are the Arizona state flower, and bloom through April and May.  Only a few bloom each night and they die the next day.  If pollination has occurred, the fruit begins growing immediately.

Mature fruit is oval and green outside, with bright red juicy flesh and literally thousands of seeds.  A host of birds and animals depend on the fruit for sustenance; as did ancient American Indian cultures, which harvested in June and July and used the flesh, seeds and juice.  Many reservation stores still carry homemade candies, jellies, juice and other products made from the Saguaro fruit, and it is becoming increasingly popular in specialty shops across the nation.

The Saguaro is home to many birds including the Gilded Flicker, Desert Woodpecker, and Purple Martin.  The birds carve their homes in the flesh of the cactus, forming holes that harden and petrify.  These are called boots, and can be found in almost any Saguaro cactus.  Some, like the Flicker, will not re-use their hole after one season.  These vacated holes are taken over by Elf Owls, finches, and other birds.  Bats, dove, and other species depend on the fruit as it is a major contributor to their diet.   

Sources

http://www.nps.gov/sagu/

http://en.wikipedia.org/wiki/saguaro

http://www.desertusa.com/du_sonoran.html

Related articles:

The Sonoran Desert

The Edible Saguaro Cactus