Cactus

Cacti are flowering plants in the family Cactaceae, a group adapted to environments where water can be scarce. Most species are native to the Americas, especially dry regions of Mexico and the southwestern United States, although some have spread or been introduced elsewhere. Their appearance varies greatly: some are tall and column-shaped, others form rounded bodies or flattened pads, and a few grow as climbing plants.

Instead of ordinary leaves, most cacti have areoles, small specialized structures from which spines, new shoots and sometimes flowers develop. The spines are modified leaves and can help protect the plant from herbivores while also reducing air movement close to the surface, limiting water loss. The thick green stem carries out photosynthesis and stores water. Many cacti are adapted to drought through several features.

Their stems can expand after rain and store water, while a waxy outer layer helps reduce evaporation. Many species use a form of photosynthesis called CAM: they take in carbon dioxide mainly at night, when cooler temperatures reduce water loss, and use it during the day to produce sugars. CAM is common in cacti but is not identical in every species.

Cacti produce flowers and fruits, and their pollination may involve insects, birds or bats, depending on the species. Some fruits are edible, including those of the prickly pear. Cacti are important in their native ecosystems and are also cultivated as food, ornamental plants and sources of useful materials. Their slow growth in some species means that wild populations can be vulnerable to habitat loss and illegal collection.