Plants that live on trees or air are either epiphytic or parasitic. Epiphytic plants are more commonly called "air plants." Epiphytic plants are different from parasitic plants in that they do not take any nutrients from their host tree. They take their nutrients from the air only. Parasitic plants also are attached to trees, but take some or all of their nutrients from the tree rather than the air.
Tillandsia cyanea is an epiphytic plant and the most popular of the air plants. Tillandsia air plants attach to trees and rocks and obtain all the minerals and water they need from the humid, tropical air that surrounds them. Cyanea features think, curved green leaves and spiked bracts that encircle large purple flowers. This plant needs a lot of moisture and thrives best if you put wet moss around the roots.
This tillandsia is actually easier to grow than cyanea, although it is much less showy. Caput-medusae has silver-colored, twisting leaves that are reminiscent of the snakes on the head of Medusa, thus giving the plant its name. Caput-medusae has a red flower stalk and a wide base.
Mistletoe is a a common semi-parasitic plant. There are many species of mistletoe, some of which even attach to cacti. Most types, however, live on trees. One of the most common types of mistletoe is Phoradendron, which means "tree thief." Phoradendron attaches itself to oak trees. Mistletoe is a semi-parasitic plant because it does go through the process of photosynthesis, which means it only gets some of its nutrients from the host tree.
Cuscuta (Dodder) is an interesting parasitic plant because its seeds to sprout in or near soil; but, after germination, the plant must attach itself to a host within 10 days or it will die. Dodder can attach to any plant, but it thrives best when attached to trees. The plant has long, thin leaves that are yellowish in color. These leaves wind their way around a plant and can crawl even to the top of a tree's canopy. A completely infected tree can look like it is covered in a long, hairy yellow wig.