BENZING, DAVID, H. Department of Biology, Oberlin College, Oberlin, Ohio 44074. - Ferns as epiphytes.
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