In contrast to the angiosperms where fewer than 10% of the species are epiphytic, more than half of the ferns fit this description. Moreover, the epiphytic ferns exhibit diverse structure and function and occupy everwet and shady to arid and fully exposed microsites. In fact, the pteridophytic epiphytes possess many of the same devices for accommodating scarce and unpredictable supplies of water and key mineral nutrients that their flowering plant counterparts employ to grow under the same conditions. In some other respects, the ferns exceed the angiosperms in adaptive versatility, for example, in the variety of ways that foliage is specialized to deal with drought. Solutions to aridity range from syndromes based on poikilohydry, deciduousness, and CAM photosynthesis, three conditions that do not co-occur among closely related angiosperms. Shade tolerance among the ferns also has both unusual anatomical and physiological bases. Mechanisms of mineral nutrition are also diverse and sometimes facilitated by the same kinds of mutualisms with animals that benefit certain epiphytic angiosperms. This report describes the nature of the forest canopy as habitat for vascular plants and how the pteridophytes parallel and differ from the seed plants in the ways that they use this widely available ecospace. Finally, aspects of the adaptive biology of epiphytic ferns that warrant additional study as examples of novel or extreme adatations are mentioned.

Key words: adaptations, epiphyte, fern, xerophytism