epiphyte

1. (botany) A plant that grows on another, using it for physical support but obtaining no nutrients from it and neither causing damage nor offering benefit; an air plant.Examples: "It has been suggested to me that these fine plants will not prove cultivable, because they are epiphytes.[…]The probability however is, that they do not require to be treated as epiphytes, and that, like orchids, they will grow better if committed judiciously to the earth."; "The nature of the surface of a plant also determines the number and sort of Epiphytes which lodge on it."

2. (biology) A fungus that grows on a plant but does not feed upon it saprotrophically (an epiphytic fungus). (The science of detecting and studying any such symbiosis as may be involved in this relationship is still developing.)