Cactus are indigenous to the Western Hemisphere, are found in their greatest concentration along the Tropics of Cancer and Capricorn, and are native to every American state except Vermont and Maine. They are found in deserts, on seashores, in mountains, on plains, balds, and glades.

     Cactus are as evocative of the West as Sagebrush is, and the two plants often grow near each other.

     Cactus come in a number of shapes, their flowers are often very large and attractive, their fruits are edible (some delicious, some not so), and they have evolved a number of structures and processes that make them perfectly at home in what we humans usually call "a hostile environment": They have a tough, waxy outer layer that reduces moisture loss; they produce chlorophyll not in leaves but in the outer cells of the stems; they convert absorbed water into a mucilaginous liquid that can be stored in large quantities in tissues capable of expanding; and many Cactus root easily into new plants from broken pads/stems of older plants.

     "Cactus" is Greek for "prickly plant"; the word was used by Linnaeus in the 18th century to describe a prickly, thistle-like Asteraceae found in Italy. The name "Cactus" was again used in the 19th century for the newly discovered spiny, drought resistant plants discovered in the Western Hemisphere.