Genus Cylindropuntia (Cholla)
The cacti of this genus usually grow in large numbers and can vary greatly in size. The spines on the cholla plants are more numerous than on any other cacti.

Genus Opuntia (Prickly Pear)
The most common cacti in the southwest of the United States, the prickly pear cacti are identified by flat, rounded sections connected at the ends. These Cacti can grow very tall and wide.

Genus Cereus (Columnar Cacti)
These tall cacti grow in columnar shapes up to 40 feet (12 meters) in height. Large white flowers appear at the tops of the columns when flowering. The well-known saguaro cactus is a member of this genus.

Genus Echinocactus (Barrel Cacti)
The spines on barrel cacti grow in vertical rows with smooth surfaces in between. Some of these species have a tuft of soft material at the top, when not flowering.

Genus Coryphantha (Beehive Cacti)
These cacti are small in size, have a dense layer of spines, and have one large flower at the top of the plant. The flower often hides the plant from view. These cacti grow among desert grasses.

Genus Mammillaria (Pincushion Cacti)
Among the smallest of the cacti, these round cacti have delicate flowers. These plants can be found near the roots of larger cacti.