Pincushion cacti are small, squat plants that usually don’t grow more than 6 inches (15 cm.) in height. They can be ball or barrel shaped, and are native to the warmer regions of the United States. The pincushion cactus plant is most commonly grown indoors but it can tolerate some chilling temperatures if grown outside. Pincushion cactus is so called because it is covered in white spines over the entire surface of the plant. It is a very prickly little specimen that is best handled with thick gloves.