Cool cacti

Long, yellow spines erupt in starry clusters from ridges on the body.

Branches can take up to 40 years to form, growing at less than 1 in (2.5 cm) a year. Vertical stems can grow up to 26 ft (8 m) tall.

Overlapping stems create a fan shape.

Paddle-shaped stems are flat, unlike stems in most cacti.

Birds such as this owl use the saguaro cactus for nesting.

With a recorded height of 63 ft (19.2 m) and a trunk about 3 ft (1 m) thick, the Mexican false saguaro is the tallest-known living cactus in the world. 63 ft (19.2 m)

Many cacti live in the desert, where their water-filled stems help them survive long periods of drought. Most plants use their leaves to make food from sunlight, but cacti do this using their green, fleshy stems. To protect themselves from hungry animals, cacti have specially adapted leaves called spines. Living in hot and dry environments means that cacti have to make the most of the rare, but often heavy, rainfall. Ribs on the barrel cactus allow it to stretch its stem to quickly take in as much water as possible. In harsh desert conditions, plants grow very slowly and live a long time. Some, such as the saguaro and false saguaro cacti, can live for up to 300 years. These tall

Flowers bloom around Christmastime in the Northern Hemisphere.

Fragrant flowers grow on top of this rounded cactus. Fiercely sharp, long spines protect this cactus.

White, hairlike spines reduce evaporation.

Red spines give this plant its name.

Flowers open at night for moth and beetle pollinators.

Stout stems can be up to 31⁄3 ft (1 m) thick.

cacti, along with the organ pipe cactus, are pollinated by lesser long-nosed bats at night, while most other species are visited by insects or birds during the day. Prickly pear flowers curl their anthers around visiting bees to coat them in pollen. Not all cacti live in the desert—the Christmas cactus, for example, grows on trees in the tropical rain forests of Brazil.