Flora contained within the Americas is rich and varied. Due to mountain ranges, vegetation changes dramatically on different sides of the mountains and as you increase altitude. The Amazon Basin to the east of the Andes is the richest floral zone in the world. This basin captures the run-off from the Andes and is a huge seven million square kilometers, with most of that covered in rainforest. The western coasts of North and South America include wet temperate rainforests, in Chile, Alaska, Canada, and the USA. The Canadian Wilderness is a vast area of temperate broadleaf forests. Cacti grow in dry and arid areas and are native to the Americas.