This exhibit shows an example of "convergent evolution." Two individual plants or animals that look alike often share close bloodlines, like sisters. But many distantly related plants, like the cactus and euphorbia in this display, may also appear almost identical.

Cacti and succulent euphorbias live on opposite sides of the Atlantic Ocean. Both inhabit very dry places. Over millions of years each has independently developed similar structures for conserving water through convergent evolution. Shallow, far-reaching roots in both capture rain as soon as it hits the ground. Thick, juicy, leafless stems store water, and spines give protection from thirsty animals.

Success breeds success and, in these desert plants, success is fleshy and spiny.