FIGURE 12.1 Similar growth forms. Cacti and euphorbs are not closely related, but they have evolved many similar adaptations that allow them to live in hot, dry environments. (a) Organ pipe cactus (Stenocereus thurberi ) in Arizona. (b) Euphorbia (E. damarana) in Namibia.
(a: Dhoxax/Shutterstock; b: Patti Murray/Earth Scenes/Animals Animals)