Mexico's prickly pear cactus: energy source of the future? The prickly pear cactus is such a powerful symbol in Mexico that they put it smack in the middle of the national flag. It was considered sacred by the ancient Aztecs, and modern-day Mexicans eat it, drink it, and even use it in medicines and shampoos. Now scientists have come up with a new use for the bright green plant: producing renewable energy.