Tropical rainforests, which are located near the equator in parts of South America, Central America, Mexico, the Caribbean, parts of Asia and Africa and Australia have warm temperatures that rarely fluctuate and rain, sometimes several times a day. Average yearly rainfall is between 66-390 inches. It is quite humid in a tropical rainforest--therefore, water is not a limiting factor for the growth of plants. Usually, the growth of plants is very lush and light is a limiting factor, as most of the available light is in the canopy and the forest floor is much darker. Therefore, plants grow rapidly, and some are epiphytes, which means they can grow on top of an exisiting plant--such as a vine, certain orchids and ferns that grow on a tree to gain access to the light above. Also, plants usually have broad leaves with many stomates, as preventing water loss is not an issue in a rainforest. Some have drip tips, a way to cope with excess water, allowing plants to shed it to avoid growth of bacteria and fungus on the surface of the plant. In the understory where it is darker, one finds shade tolerant shrubs, herbs, and vines capable of climbing trees to reach the light. In the canopy, one finds broad-leaved evergreens, and epiphytes that grow on top of them to reach the light. Some trees have buttress roots, these create a spread--out root network near the surface, to allow an efficient uptake of nutrients because tropical rainforest soil is nutrient poor, growth of plants is fast and competition is fierce. These roots support plants better in this moist environment, and also minimize soil erosion.