American Cacti
With only a few exceptions, the true cacti are found exclusively in the western hemisphere, from Canada to the southern tip of South America, the West Indies, and the Galápagos Islands. Cacti are often referred to as xerophytes, plants adapted to extremely dry conditions and capable of withstanding drying for extended periods. The most obvious characteristic of cacti are the spines, which serve a number of purposes besides protection, such as casting shadows on the cactus to protect it from the sun, reducing leaf surface area, which reduces water loss, and serving as points of condensation for moisture, which then drips down for use by the roots. Christmas Cactus The Christmas cacti are a group of bushy perennial cacti growing to a height of about 16 cm (5 in). These cacti are often found in shaded areas in rich, well-drained soils. Organ Pipe Cactus The organ pipe cactus grows in parts of Arizona, Baja California, and northern Mexico at elevations below 1000 m (3000 ft). The organ pip