An epiphyte is any plant which grows on the surface of another plant. The word is derived from the Greek, epi- (meaning "upon") and phyton (meaning "plant"). Epiphytic plants are often called "air plants" because they do not root in the soil but instead on another plant. True epiphytes are not considered parasites because they pull moisture from the air or dampness from the surface of the plant they are living on and do not take any needed nutrients from the host plant itself. Because their primary water source is the air and dampness on the surface of their host plant, epiphytic plants are most commonly found in tropic and temperate rainforests. Although the term most often refers to higher order plants, epiphytes include mosses, lichens, and algae.
Although epiphytes grow on other trees and plants non-parasitically, there is evidence that moss and bigleaf maples have a symbiotic relationship. The bigleaf maple sends out "canopy roots" through the moss to collect the nutrients that the moss collects from the air, water, and soil (Storer, et al, 2004, p. 154).
Examples of epiphytes at IslandWood:
Source regarding evidence of symbiosis with big leaf maple:
Storer, T.I. Usinger, R.L. Lukas, D. (2004) Sierra Nevada Natural History. California: University of California Press.