Cactus

A cactus is a kind of plant that is built to live in dry places. Most cacti grow in the deserts of North and South America. They are famous for their thick green stems and their sharp spines. There are about 1,750 different species of cactus. They come in many shapes, from tiny buttons the size of a coin to giant towers taller than a three-story building.

Cacti look strange because they have given up something most plants have: leaves. Wide flat leaves lose a lot of water to the air. In a desert, that water is too precious to waste. Over millions of years, cactus leaves slowly changed into spines. The thick green stem took over the job of making food from sunlight. This is why a cactus looks so different from a rose bush or an oak tree, even though all three are flowering plants.

The stem of a cactus is more than just green skin. Inside, it works like a sponge. When rain finally falls in the desert, the cactus soaks up water through its shallow roots and stores it in the stem. The stem swells up like a water balloon. During long dry months, the plant slowly uses that water to stay alive. A waxy coating on the outside keeps the water from leaking back out.

Spines do several jobs at once. They protect the cactus from animals that would chew into it for water. They also shade the stem from the burning sun. On some kinds of cactus, the spines even catch drops of fog and guide the water down to the roots.

The biggest cactus in the world is the saguaro. It grows in the Sonoran Desert in Arizona and Mexico. A full-grown saguaro can stand 40 feet tall and weigh more than 4,000 pounds, about as much as a pickup truck. Saguaros grow very slowly. In its first 10 years, a saguaro might be only an inch or two tall. It takes about 70 years before it grows its first arm.

Cacti also bloom. Their flowers can be bright pink, yellow, white, or red. Some open only at night and are pollinated by bats. The fruit of the prickly pear cactus is eaten by people and animals across Mexico and the American Southwest. Hummingbirds, bees, and woodpeckers all depend on cactus flowers, fruit, and shade. In the desert, the cactus is not just surviving. It feeds a whole community.