The study of plants is called botany. Each climate has its own particular botany, so if you study desert growth, you might focus on such plants as cactus and sage, while if you're in the jungle you'd study the lush growth there.
Someone once said, "Botany is the science in which plants are known by their aliases." Indeed, the study of botany includes learning the scientific names of plants. The origin of the word botany came from the Greek word botane, which means "grass" or "pasture." Since the original meaning focused on the idea of a pasture, it's possible the study of botany came about from herdsmen needing to know what plants were safe for their herds to eat.