Characteristics: Most cactus are stem succulents. They have fleshy stems. Most have very little woody tissue. They never have leaves. Cactus spines probably evolved from leaves. Most cactus cannot remove water from cold soils, so they are dormant in winter and grow in summer.

Size: Cactuses vary widely in size and shape. The giant saguaro looks like a bare tree with thick, upturned branches. They can grow as tall as 60 feet (18 meters). Other cactuses are less than 1 inch (2.5 centimeters) high.

Where Do They Grow? Most cactus species grow in hot, dry regions. They are common in Mexico and the Southwestern United States. They can also be found on mountains, in rain forests, and the polar regions.

Some cactuses are fluted or ribbed. Some have shapes called tubercles. In tubercles, the areoles are at the tips.

All cactuses produce flowers. They can usually be seen on the areoles. Flowers can be white or a bright color such as yellow, orange, red, or lavender. For most cactuses, flowers only bloom for a few days. Some flowers open only at night.

Cactuses have extremely long roots to reach out through the sandy, rocky soil. These roots grow close to the surface collecting water. A large saguaro may have root systems that are 50 feet (15 meters) long. After a heavy rain, these roots soak up and move large amounts of water to the plant stem.

Life Cycle: All cactuses reproduce. Their flowers have both male and female parts. The male part yields pollen. The female part contains an egg. Birds, bats, and insects are attracted to the colors or the scent of the flowers. While feeding, these creatures transfer pollen from one part to other parts of the plant. This process is pollination. This causes a fruit to develop. This cactus fruit is a fleshy berry that contains seeds. Seeds are scattered by birds, wind, and rain. A cactus plant may produce about million seeds. Only one or two seeds will live to become a new cactus.

Some cactuses reproduce without seeds and flowers. Both prickly pear and cholla cactuses have stems with weak joints. When a stem breaks off, it sometimes grows in the soil and becomes a new plant.

Most cactuses grow very slowly. It could take a year to grow 1 inch (2.5 centimeters). Older plants may grow 3 or 4 inches (7.5 to 10 centimeters) each year. They can live 50 to 200 years.

Kinds of Cactuses: Some of the most common cactuses found in the Southwestern United States include the barrel, prickly pear, organ pipe, cholla, barrel, and saguaro cactuses.

Saguaro, organ pipe, and barrel cactuses are members of the same family. The saguaro, pronounced se-WAR-oh, may have as many as a dozen armlike branches. The main stem can reach 40 to 60 feet (18 meters) high and 2 feet (0.6 meter) in diameter. Saguaro provide homes for many birds such as Gila woodpeckers, gilded flickers, elf and screech owls, purple martins, and house finches. A fifty foot saguaro (Left photo) weighs as much as nine tons. It can live for as long as 200 years.

The organ pipe cactus (Shown above right) has tall stems that grow in groups. They look like the pipes from an organ. They have slender arms. Branching is a way to increase their surface area and food production. They are found only in places like southwestern corner of Arizona and northern Mexico.

Chollas and prickly pears are members of the same family. Stems of the jumping cholla, or chainfruit cholla, fall off easily. Some people say they 'jump' on people as they walk by. Teddy bear cholla have light brown, sharp spines that pierce tender skin. They are hard to get out. From a distance, they look soft like a teddy bear. These chollas grow to about 5 feet (1.5 meters) tall.

Desert packrats create their dens with cholla joints and other things such as sticks and prickly pear pads. They build tiny tunnels to protect themselves from foxes, coyotes, and other predators. Some of these nests are hundreds of years old. They are dirty and unhealthy, so don't touch them.

Prickly pears are many-branched. Prickly pear branches, often called pads, are flattened and look like overgrown, fleshy leaves. They have large spines as well as clusters of easily detached tiny spines called glochids. These glochids are barbed, very small, and hard to remove when stuck into skin.

The fruits of prickly pear are juicy and edible. They must be carefully peeled before eaten. Some people also gather, cook, and eat the pads of prickly pear as a vegetable.

Some animals such as javelinas love to eat prickly pear cactus. You can sometimes see the bite marks on the cactus.

Value of Cactuses: Cactuses are important to animals and people. Small animals, insects, and birds eat their stems and flowers. Birds build nests in cactus stems. Both birds and animals hide in cactus plants.

Cactuses are also a food source for people. People eat cactus fruits or grind the seeds into a meal for cakes. Some cactuses are used to make red food dye. And other cactuses are used as lumber.

Mistaken for Cacti: Newcomers to the Southwest US are sometimes confused by plants that they think are cactus. 'Not-cactus' plants include Century plants, hen-and-chicks, yuccas, sotol, bear grass, desert pineapple and ocotillo.

Examine the photo of the 'Desert Garden' at the top of this page. Can you identify any non-cactus plants?

More Information

• Go to the In Depth Page
• Go to the WebQuest Page

 

Note: All photographs taken with a digital camera in Arizona, New Mexico, Utah, and Texas.
Developed by Annette Lamb and Larry Johnson, 05/02.