This series of stamps pays tribute to the species of plants that have adapted over the eons to withstand the harsh environment of the desert. Surviving through extremes of temperature and very little rainfall, the cactus has adapted and flourished. Pictured are the Barrel Cactus, Agave, Beavertail Cactus, and the Saguaro. The latter is the largest cactus native to North America - often reaching a height of 60 feet and a weight of more than three tons.