Did you know all cacti are succulents, but not all succulents are cacti? With 2500 species, cacti all have three things in common:

1. Spines are modified leaves with important jobs. Some spines are obvious – long and sharp. Some look like a light covering of snow. Spines protect these plants from predators, allow for a method of transportation (imagine small cacti hooked on a cowboy’s jeans), and oddly enough, shade the plant on hot, sunny days. Spines, however, do not aid in photosynthesis as leaves would. The fleshy stems perform this job.
2. A waxy coating on the pads or stems reduces evaporation. Cacti do their breathing at night. During the day, sunlight is gathered by the plant through its stomata (think of a closed window below the surface of the stem). Transpiration occurs at night when it’s cool enough for the plant to open the stomata to let out oxygen. This is called Crassulacean Acid Metabolism, or CAM photosynthesis.
3. Shallow roots quickly absorb any available moisture. Cacti can grow root hairs in a matter of hours when the plant senses moisture. These root hairs dry up when they are no longer useful. Many cacti also have a tap root longer than the height of the plant, allowing them to reach water sources underground.

Not all cacti are found in arid regions. Some are epiphytic and found in tropical rainforests.