There are also many orchids which do not grow on trees at all, but only on specific kinds of rocks. These plants are called Lithophytes. The term comes from the Greek words, litho-, meaning stone and phyte, a plant--thus a plant that lives on stones. Often they are found around the bases of trees or in crevices on rocky hillsides where pieces of debris collect.
Many of these orchids can be grown as epiphytes on cork rafts, on tree fern, or open baskets. An example of a Lithophyte is Sophronitis.