Plants On Plants: An Introduction To Epiphytes

If you take some time out of your day and observe those green and brown things that grow all around us—yes, the plants—you will find that the plant world is full of weird, wonderful, and fascinating species. You get the standard ones that root in soil and can become magnificent trees or remain small herbs; there are carnivorous plants that eat insects; and there are plants that grow and spend their entire lives on other plants. Yes, you heard that right! Plant species exist that do not ever need to root in soil to survive, instead having evolved features that allow them to grow on other plants. Such plants can be categorized into two classes: parasites and epiphytes. Parasitic plants, like mistletoes and dodders, derive nutrition and even water from the plants that they grow on (which are called “hosts”), eliminating their need for contact with soil. Epiphytes, on the other hand, only use host plants as a means of support. A look up at trees, especially in tropical forests, will reveal these plants to you—orchids, ferns, and even moss are examples of epiphytic flora, found on tree branches, trunks, and, if you look closely, in crevices. Epiphytes have a bunch of cool adaptations that allow them to access water and nutrients to make their own food, all while living on other plants. Read on to find out how they manage to do this!

But first—which plants are actually epiphytes?

Epiphytic plants together form a very large and diverse group, encompassing many different kinds of life-forms. A simple division of this group would be a split between “vascular” and “non-vascular” epiphytes. Non-vascular epiphytes are “simpler” plants that do not possess xylem and phloem, the tissues that allow other plants to transport water and nutrients between their buried roots and topmost leaves (Whitton, 2013). As a result, these plants are really small in size and grow in mats, often not looking like plants at all! The most common member of this group is moss, that soft, green plant which adds a layer of texture to tree bark and branches, rocks, walls, or any moist surface, really. Moss belongs to a class of plants called bryophytes , which also includes two other groups—liverworts and hornworts—all of which together make up the group of non-vascular epiphytes (Whitton, 2013).

Vascular epiphytes, on the other hand, do possess specialized tissues that allow them to transport water and nutrients, resulting in structurally stronger and bigger plants. These plants can be categorized into those that produce flowers and reproduce through seeds, called the angiosperms, and those that do not produce flowers and instead reproduce through spores, a more primitive form of seeds. Ferns constitute the spore-producing group of vascular epiphytes, easily distinguished by their pretty, patterned leaves, occasionally with rows of spores that look like small dots on their undersides.

Flowering epiphytes include many charismatic species that are often prized as ornamental plants. Many orchids known for their uniquely shaped flowers, bromeliads (which are closely related to the pineapple plant), and “air plants” are part of this group. Keep a look out for these plants the next time you visit an herbarium or botanical garden; you are sure to catch a glimpse of these beautiful flowers!

So, how do epiphytes manage to live on other plants?

Now that we know which plants live as epiphytes, let’s find out how they actually manage to do so. The biggest difference between epiphytes and terrestrial plants is the lack of access to ground soil, the main source of water and nutrients for most plants, which, along with sunlight, allows them to make their own food. To overcome this challenge, epiphytes have evolved a number of adaptations that allow them to access these resources from other sources (Benzing, 1998).

The two primary sources of water for all epiphytes are rainfall and the atmosphere. Vascular epiphytes have specialized leaves and roots with fine hairs, called trichomes, that allow them to directly absorb rainwater and water vapor that is present in the atmosphere for their use. The roots of these plants also serve as an anchor, wrapping around tree trunks and growing into tree cavities, providing them the support they need to grow on vertical surfaces. Decomposing matter on tree trunks and in cavities, as well as the minerals in rain water and water vapor, give these plants the nutrients they need.

Upon looking closer at tiny non-vascular epiphytes, we can see a mass of miniscule leaf-like structures and fine hairs called “ rhizoids ,” all of which work hard to absorb and retain water and minerals, mainly from rain. Because of their strong dependence on rainfall and the atmosphere, epiphytes are usually found in more wet and humid locations, where there is a constant supply of water. This is especially true for bryophytes, which cannot extend roots to search for and transport water. Many epiphytes also like to grow high up in tree canopies, which gives them good access to sunlight, giving them an advantage over other plants that grow on the dark forest floor!

Why are epiphytes important?

Though epiphytes might seem like just another group in the dizzying number of plant species out there, they perform many functions that are unique to them. Something you may not expect is that epiphytes are very important for many animal species that share their ecosystems. One way in which epiphytes help animals out is by providing them with habitats—a safe place to live, reproduce, and grow. The “tank bromeliads” found in South American forests, so called because of the large amounts of water that they collect between their leaves, are known to support entire ecosystems! Many species of insects, spiders, scorpions, worms, and even crabs make their homes in the pools of water these plants collect in the crooks of their leaves, living tucked away in the canopy. Even frogs and lizards use epiphytes, taking advantage of the cool microclimate provided by these plants to take shelter and lay their eggs. The stems, fruits, and leaves of epiphytes and the insects that live in them were also found to be an important source of food for many birds (Nadkarni, 1989).

Because they rely primarily on the atmosphere and rain for water and nutrients, epiphytes are especially sensitive to shifts in temperature, rainfall, humidity, and other changes in climate. It is for this reason that scientists are studying epiphytes to understand if and how climate change is impacting forests (Andama et al. 2003). If we lose epiphytes, we not only lose some very beautiful plants, but also the fascinating creatures that rely on them. It is for this reason that it is important to understand these plants better and increase awareness about them. So be sure to spread the word!

Flesch Kincaid Grade Level: 11.1

Flesch Kincaid Reading Ease: 56.6

Glossary

Adaptation: The presence of specific features or certain habits which enable a plant or an animal to live in its surroundings

Humid: Containing a high amount of water or water vapor

Microclimate: The climate of a very small or restricted area, especially when it differs from the climate of the surrounding area.

Bryophytes: A group of non-vascular plants, that is, plants that lack the xylem and phloem networks that allow vascular plants to transport water and nutrients internally; includes mosses, liverworts, and hornworts

Rhizoids: Root-like structures on mosses