Epiphytic plants, such as various species of orchids (Orchidaceae), grow upon another plant, using the plants for physical support, but bringing no harm to the host plant. This is an example of which symbiotic relationship?

The correct answer is commensalism.

Explanation:

Commensalism is a type of symbiosis in which an association of two different organism takes place but only one get benefits and other neither benefited nor harmed. It is different from parasitism as in it host does not harm by the other organism. However, in mutualism both the organism benefited by the association.

Orchid plants exhibit commensalism with other plant or tree for support but no harm is done by the orchid to the tree.

Thus, the correct answer is commensalism.