What is a cactus?

Cacti come in all shapes and sizes, but nearly all of them have large swollen stems that allow them to store water. This is because many cacti grow in areas with little or no rainfall for long periods of time. Desert cacti have clever adaptations to help them survive extreme heat and drought, however a few very different cacti live in rain forests.

Summer flower ❯ The monk’s hood cactus produces pale yellow flowers throughout the summer. They are pollinated by insects and produce spiky fruits.

Mass of thin roots. Water is stored in the barrel-shaped stem. Some cacti, such as this one, expand when filled with water and contract when dry.

Roots ❯ The roots of this cactus spread across a large area and grow close to the surface. They quickly draw in as much water as possible from rain or dew.

Spine ❯ These help shade the stem and stop animals from eating the cactus. A spine is, in fact, a type of modified leaf with a small surface area to prevent water from evaporating.

The ribs channel dew to the roots.

Flakes ❯ In a desert, the sun is very bright. White flakes grow on the stem of the cactus, helping to reflect light.

Cacti shapes

Columnar Cacti, such as the saguaro, can grow 40 ft (12 m) tall, and have distinctive armlike side branches. Bats pollinate their flowers, which grow at the top of the plant.

Clustering The prickly pear cactus has flattened stems that grow in clusters. The red, prickly fruit must be peeled to remove the small spines.

Globular Many cacti, like the barrel cactus, have rounded stems. This maximizes water storage, while its vertical ridges direct every drop of water to the roots.

Climbing Some cacti live in forests, where they clamber up other plants for sunlight. The queen of the night cactus has huge flowers that bloom for just one night.

Deserts Desert cacti have to survive extreme heat and light. Often large and spiny, they grow all over North and South America.

Forests Some cacti grow in shaded forests. Their stems do not need to store water, as the roots draw moisture from the air.

Grasslands Smaller cacti often grow in grasslands, where the grasses shade them in summer. Most are found in South America.

Where do they grow?