Succulent or Cactus?

This winter the Conservatory features the “Crash Landing” display, which shows off dozens of cacti and other succulents among flying saucers to evoke an arid setting not unlike that of Roswell, New Mexico.
We are often asked, “What is the difference between a cactus and a succulent?” The answer is that all cacti are succulents, but not all succulents are cacti. Both have fleshy leaves and/or stems that store water and are adapted to survive in harsh, dry environments. Both grow in similar conditions: full sun and well-drained soil that never stays wet. Surprisingly, many are well-adapted to very cold temperatures. Deserts, after all, can get chilly once the sun goes down.
Cacti are a subset of succulents. They are all in the Cactaceae family, defined by the presence of a structure called an areole. It looks much like a small raised dot or a patch of cotton, out of which grows a spine or cluster of spines.
Many non-cacti succulents may have spines or thorns, but only a plant with an areole at the base of that spine is a cactus. Additionally cacti are native almost exclusively to the Americas.
— Aaron Steil, Manager of Public Programs