Epiphytic plants are plants which rely on other plants for support, growing on trunks and branches rather than rooting themselves to the ground, or the seafloor, in the case of aquatic epiphytes. It is estimated that there are around 30,000 epiphytic plant species around the world, with around half of those species dwelling in the rainforest. The proliferation of such plants illustrates how very effective their lifestyle can be.
These plants are not parasitic: they do not derive any nutrients from their hosts. Instead, they gather nutrients from the air or water around them, relying on their host to provide physical support in the form of a place to call home. Epiphytic plants come in a wide array of shapes, sizes, and colors, all of which produce copious seeds to ensure that the plants continue to survive. Unlike plants on the ground, epiphytes cannot count on a high germination rate, as their seeds have to land in just the right spot.
In the rainforest, epiphytic plants collect in the forest canopy. Because they can grow up in the air, they can position themselves in a sunny location, putting them at an advantage over plants on the ground, which are heavily shaded. Living in the canopy also gives epiphytic plants access to an array of animals and insects rarely seen near the ground, and to more water. Many animals use epiphytes in the rainforest as habitats, living in the hollows created by their leaves.
Orchids are a very well known group of epiphytes, as are bromeliads. These tropical plants are physically quite striking, and they are popular houseplants as well. Epiphytes can also be found in the ocean, attaching themselves to various seaweeds, and in temperate forests. These plants are considered by some researchers to be a great example of convergent evolution, as numerous plant species adapted epiphytic characteristics, suggesting that the epiphytic lifestyle is a logical progression in plant evolution.
Although epiphytic plants are not parasitic, they can still harm their hosts. Some strip protective bark away as they put down roots, for example, and many shade the leaves of their hosts, preventing them from photosynthesizing. Epiphytic plants can also attract insects which may damage a tree, and they can increase wind resistance, which can be dangerous for trees in windy areas. Naturally, epiphytes do not want to kill their hosts, however, so many have evolved to live as symbiotically as possible in a mutually beneficial relationship. For example, epiphytes can store water and nutrients which can be used by their hosts.