What is an Epiphyte?

 

The word, epiphyte, is derived from two Greek terms, epi- and phyte, literally meaning “that which is found above or on a plant.”  The term is not exclusively botanical and can broadly include epiphytic snails on grasses!  However, among botanists, the term refers to plants that perch on other plants.  Historically, the word, epiphyte, has been used almost exclusively as an epithet for plants with a mutualistic or commensal association with their hosts:

Mutualistic to its host, providing services that the supporting plant would not have otherwise (e.g., mosses to prevent host dessication and certainorchids to attract pollinating euglossine bees to Brazil Nut trees)

Commensal to its host, offering neither benefit nor detriment while taking support (e.g., Spanish Moss, a member of the pineapple family and not a moss at all)

In other words, as botanist David Benzing wrote in his 1990 book, Vascular Epiphytes, “True epiphytes routinely spend their entire lives without contacting either forest floor or host vasculature.”

Yet, after centuries of exploration and laboratory investigations, ecologists have learned two important lessons about organisms: living things are sometimes difficult to pigeon-hole into taxonomic systems, and they manifest a spectrum of responses to their surroundings rather than a strict black-and-white dichotomy often found in textbooks and field-guides.

Are there parasitic epiphytes?  That is, are there plants that show features commonly associated with epiphytes and that also exploit their supporting hosts for water and/or nutrients?  Most biology primers state unequivocally that the terms are mutually exclusive.  If a plant is an epiphyte, then by definition it cannot also be a parasite.  Nevertheless, there is a wide spectrum of “suspect” associations that are neither commensal nor mutualistic.  What about mistletoes, tapping into their host’s food and water systems via specialized attachments called haustoria that act like a leach’s mouth on the supporting plant?  What about strangler figs that wrap their feeder roots around their hosts for support and then out-compete them for sunlight?  What about achlorophyllous (i.e., without sugar-producing pigments) orchids that take nutriment from their hosts indirectly through specialized fungal interactions?  What about numerous bromeliad tanks crowded so closely together that they collectively cause the branches of the host tree to snap off under their tremendous weight?  Do these plants display features often associated with parasitic organisms?

Parasites, commensals, and mutualists are all part of a continuum of interrelationships among organisms.  That continuum is called symbiosis.  As Lynn Margulis, distinguished professor in the Botany Department at the University of Massachusetts, asserted in the periodical BioScience in 1990, “symbiosis [sic] refers to protracted physical associations among organisms of different species, without respect to outcome.”  In the life sciences, words are battle cries for entrenched (and often static) viewpoints.  Life itself resists the obscurity of our nomenclature and unsettles us by its diversity.  The three categories of symbiosis are unavoidably fuzzy and cannot be delineated with any amount of finality.  Perhaps it would be more constructive just to drop the words, parasitic, commensalistic, and mutualistic,from our vocabulary and use the more expansive term, symbiotic, to describe organisms’ interrelationships. 

What are some other examples of epiphytes apropos to the mission of Selby Gardens?  Members of the pineapple family, bromeliads are abundant epiphytes through the New World tropics.  Their overlapping rosettes of leaves often form tanks or cisterns of water high off the forest floor and provide important aquatic habitats for insects and frogs.  The orchid family, perhaps the largest family of flowering plants on Earth, contains numerous, even spectacular, epiphytes!  Other epiphytic plants include ferns, liverworts, philodendrons and other aroids, even cacti (e.g., Christmas cactus) high up in tropical forest canopies where the intense equatorial sunlight provides ideal dry habitat.   

Epiphytes are often slow-growing with thick, waxy leaves and unusual roots.  Their dispersal methods vary from clouds of microscopic fern spores or millions of dust-sized orchid seeds to plumed or fleshy seeds of bromeliads dispersed by winds or hungry animals.  Epiphytes interact with their surroundings in complex ways, too.  Some contain ant nests, many hold gallons of water, still others capture forest debris that eventually becomes soil.  Many epiphytes have root systems containing fungi called mycorrhizae that aid in the uptake of scarce nutrients.  Epiphytes occur in many regions of the world, even well into temperate zones; but they reach their greatest diversity in the wet tropics.  On tropical mountainsides that face prevailing winds, they sometimes become so lush that we can hardly see the original host tree! 

Artificial propagation of epiphytic plants is an important component of the professional nursery trade in Florida.  Some are cultivated or mounted in pots or in the ground.  However, in the wild, many of these same species may live 100 feet off the forest floor!  Their unusual leaves and flowers, their resistance to drought, and their eye-catching character make epiphytes among our most popular plants.  Regardless of their types of symbiotic relationships, help us with our mission to conserve epiphytes and their habitats, many of which are at-risk worldwide, by becoming a member of the Marie Selby Botanical Gardens!