Vascular epiphytes do not share distinguishing systematic or biological profiles. Taxonomic participation is broad although the group is dominated by higher ferns, members of a few dicot families and monocotyledons, particularly orchids. Except for some general features that promote anchorage in tree crowns and aerial dispersal of diaspores, forms and life processes associated with epiphytism also occur in soil-rooted flora. Among the more pervasive characteristics of canopy-dependent vegetation are drought tolerance and mechanisms promoting access to unusual sources of nutrient ions. Trophic mutualisms are especially common and diverse with ants playing a dominant role. Specific types of epiphytes are described along with associated water ion balance mechanisms. Research topics that seem most likely to reveal significant information on the vegetative basis of epiphytism are identified.