Epiphytes
For plants, it's all about light. Since green plants feed on light, it is important not to be covered, but to be in the light. The existence of trees is therefore about competition for light. Because of this, forests can be quite dark as the sky is effectively covered by foliage.
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Those plants that can grow on other plants (usually on trees) get an advantage. They are called epiphytes. Unlike parasites, they just live on, not off, other plants. They get closer to the light, but that also means they have trouble getting enough water and nutrients. There is little or no soil up in the trees and the roots of the epiphytes rarely reach the ground.
Many epiphytes therefore have special water-collecting parts. Orchids have stems that store water and aerial roots with special tissue that quickly and easily absorbs water and nutrients. Others, such as some pineapple relatives, have leaves that form a bowl where water can collect when it rains and they have roots down into the bowl. Because rainwater contains very few nutrients, certain epiphytes, such as pitcher plants, solve their nutrient uptake by capturing and utilising nutrients in insects or other small animals. They become 鈥渃arnivorous鈥�.
Epiphytes are most common in areas where there is a lot of rain and several unrelated groups contain epiphytes. Here in Norway, mosses and lichens are the most common epiphytes.