Epiphytes are plants that grow on other plants. They use their host plants for physical support, but do not parasitize them for nutrients. Epiphytes are an incredibly diverse group of plants that can be found growing on trees, shrubs, and even other epiphytes in tropical, subtropical, and temperate regions around the world.

Unique Adaptations of Epiphytes

Epiphytes have evolved fascinating adaptations that allow them to survive mounted on other plants. Here are some of their unique features:

Aerial Roots

Most epiphytes have developed specialized aerial roots that enable them to attach securely to their host plants. These roots differ from regular roots in that they are adapted to absorb moisture and nutrients from the air and rain rather than from soil.

• Some epiphytes like orchids have thick, velamen roots with specialized spongy tissues that can efficiently trap moisture and absorb nutrients.
• Other epiphytes like bromeliads have specialized holdfasts or clinging roots that tightly anchor the plant to the bark.

Water Storage

Since they are not rooted in soil, epiphytes need specialized structures to store water.

• Bromeliads have tightly overlapping leaf bases that form reservoirs or “tanks” that can hold rainwater and debris.
• Orchids, peperomias and other succulent epiphytes have thick, fleshy leaves and stems that can store moisture for extended periods.
• Some epiphytes even have water-filled bladders or pseudobulbs that serve as cisterns.

CAM Photosynthesis

Many epiphytes use Crassulacean Acid Metabolism (CAM) photosynthesis to limit water loss. This adaptation allows the plants to keep their stomata closed during the day to reduce transpiration. They take in CO2 and perform photosynthesis at night when temperatures are lower.

High Light Tolerance

Since they grow atop other plants, most epiphytes are adapted to high light intensities. They typically have thick, waxy cuticles and reflective leaf surfaces that protect against UV damage and desiccation.

Slow Growth

Epiphytes tend to grow very slowly compared to grounded plants. Their growth is limited because they have restricted access to soil nutrients and water. Growing slowly helps them survive on limited resources.

Small, Leathery Leaves

Many epiphytes have small, thick, leathery leaves that reduce transpiration. Others like Spanish moss have tiny scale-like leaves that minimize water loss.

Camouflage

Some epiphytes blend in with the bark or foliage of their host plants as a form of camouflage to avoid herbivory. Their greenish or brownish hues can closely match the tree canopy.

Reproductive Adaptations

Epiphytes need efficient ways to disperse since they cannot root into the ground. Many like orchids and bromeliads produce large quantities of lightweight seeds equipped with fluffy hairs that aid wind dispersal.

Types of Epiphytes

There are thousands of epiphyte species belonging to a diverse array of plant families. Here are some of the major types:

Orchids

Orchids (Orchidaceae family) comprise the most diverse and widely distributed group of epiphytes. There are over 20,000 species growing on every continent except Antarctica. They are found in a vast array of shapes and sizes, from giant Specimen Orchids to tiny Jewel Orchids.

Bromeliads

Bromeliads (Bromeliaceae family) are a tropics-loving group of around 3,000 species. Popular varieties include the spiky Pineapple Plant (Ananas comosus), colorful Puya raymondii, and tank-forming Aechmea. They can be found gripping onto trees or rocks from the southern United States to South America.

Ferns

Many tropical ferns in the Pteridaceae, Polypodiaceae, and Aspleniaceae families grow as epiphytes. Staghorn Ferns, Birdsnest Ferns, and Elkhorn Ferns are common examples. They typically have leathery or hairy fronds and wiry roots to attach to trees.

Air Plants

Air plants, also known as tillandsias, comprise over 650 epiphytic species in the Bromeliaceae family. Unlike most bromeliads, air plants do not form tank-like reservoirs. Spanish Moss is perhaps the most famous air plant. It festoons trees with its wispy grey strands throughout the Southeastern United States.

Peperomias

The Peperomia genus contains over 1,000 epiphytic species. Popular varieties like Watermelon Peperomia and Raindrop Peperomia are prized for their fleshy, colorful leaves. They originate from tropical regions of Central and South America.

Mosses

While not vascular plants, many moss species in the Bryophyta division grow as epiphytes, especially in temperate and tropical rainforests. Peat Mosses, Cushion Mosses, and Apple Mosses are common epiphytic bryophytes.

Lichens

Lichens are symbiotic organisms composed of a fungus paired with an algae or cyanobacteria. Many lichen species form leafy or crusty growths on trees, rocks and even moss. Lichens are extremely efficient at absorbing moisture from the air.

Benefits of Epiphytes

Far from being freeloaders, epiphytes confer many benefits to tropical forest ecosystems:

• As canopy dwellers, epiphytes play critical roles in water and nutrient cycling high up in the forest strata. Their roots trap falling leaves and debris, releasing nutrients as they break down.
• Accumulated organic matter in epiphyte mats holds water like a sponge during rains. The water is slowly released back to the canopy during dry periods.
• Epiphytes provide key microhabitats for arboreal reptiles, amphibians, insects, and other organisms. Their water reservoirs in particular support diverse aquatic food chains.
• Many epiphytes have beautiful flowers that attract pollinators like birds, bats, and insects to the high canopy.
• Epiphyte roots, leaves, and accumulated debris provide nesting materials and shelter for birds, mammals, and invertebrates.
• Large epiphyte mats can stabilize trees during high winds and heavy rains, reducing the chance of windthrow.

Where Do Epiphytes Grow?

Epiphytes colonize a variety of arboreal habitats:

Trunks

Most epiphytes establish themselves first on tree trunks. The rough, grooved bark provides handholds for seeds and organic matter. Humidity is also higher closer to the moist forest floor.

Branches

As epiphytes grow, they may climb out onto larger branches seeking better illumination. Mats of vegetation can build up in branch junctions.

Canopy

In wet tropical forests, branches high in the canopy support incredibly diverse epiphyte assemblages. Filtered light and abundant moisture nurture mosses, ferns, orchids and bromeliads high in the forest strata.

Emergent Trees

The crowns of tall emergent trees soaring above the main canopy host many epiphytes. Unobstructed sunlight and windblown debris allow giant air plants and orchids to flourish.

Nurse Logs

Fallen logs in tropical forests are often cloaked in epiphytic vegetation. The decaying bark provides an ideal moist, shaded nursery for young epiphytes to establish before climbing higher into the canopy.

Epiphyte Ecology

Understanding ecological concepts helps illuminate how epiphytes survive and interact with their arboreal environment:

Commensalism

Most epiphytes are commensal organisms that benefit from their host tree without impacting it negatively. They gain a raised perch and shade while the tree loses little from harboring them.

Succession

Epiphyte communities change dynamically as trees age. Pioneer species colonize young trees, altering bark and canopy conditions for later epiphytes. Diverse mats develop on mature trees.

Zonation

Distinct vertical epiphyte zones often emerge on trees, dictated by factors like light, temperature, and moisture. Lichens and mosses cling to lower damp trunks while orchids populate the sunny upper canopy.

Keystone Structures

Accumulations of organic debris in epiphyte mats are vital for trapping moisture and nutrients. Removing this material can cause communities to collapse.

Biodiversity Hotspots

Epiphyte laden trees support incredibly diverse ecosystems. A single rainforest tree in Ecuador was found to host over 900 insect species living amongst its epiphytes!

Nursery Hosts

Many trees support specific epiphytes during vulnerable life stages, providing natural highchairs where juveniles can establish away from forest floor threats.

Nutrient Cycling

Shed leaves and throughfall are captured by epiphytes. Foliar uptake of nutrients like nitrogen allows epiphytes to flourish while returning nutrients to the canopy that would otherwise be lost.

Threats Facing Epiphytes

These sensitive and intricate communities are facing many anthropogenic threats:

• Deforestation eliminates the forest canopy habitat epiphytes depend on. Selective logging is also very disruptive.
• Fragmentation makes seed dispersal between remaining forest patches difficult for epiphytes.
• Climate change alters temperature, precipitation, and humidity regimes epiphytes are adapted to.
• Invasive species like Kudzu can engulf trees, shading out epiphyte assemblages.
• Air pollution can damage sensitive epiphytic bryophytes like mosses. Nutrient deposition also shifts species compositions.
• Overcollection for the horticultural trade has decimated some rare orchid species. Poaching continues to threaten slow-growing endemics.
• Cattle grazing allows invasive grasses to establish that fuel intense fires which can incinerate epiphytes high in the canopy.

Conservation Strategies

Protecting remaining epiphyte habitat is crucial for preserving these unique plant communities. Some key conservation strategies include:

• Establishing legal protections for reserves safeguarding primary forests with intact epiphyte assemblages.
• Using canopy walkways and towers to access and study epiphytes scientifically while minimizing disruptions.
• Propagating rare epiphytes like orchids at botanical gardens to reduce pressure on wild populations.
• Controlling invasive species that compete with native epiphytes and alter microclimate conditions.
• Reforesting clear-cut areas, employing artificial “nurse logs” that young epiphytes can colonize.
• Modeling climatic shifts to identify refugia that will remain hospitable to epiphytes as climate changes.
• Monitoring epiphyte health as an early indicator of environmental change since they are so sensitive.
• Educating the public on the ecological value of epiphytes and the threats they face.
• Incorporating epiphyte protections into forest management plans and operations.

Cultivating Epiphytes

Many epiphytes can be grown horticulturally as striking, low maintenance houseplants. Here is some advice for cultivating them:

Provide Bright Light

Most epiphytes naturally grow in shaded tropical canopies and cannot tolerate direct sun. But they do require bright, filtered light. East or west facing windows are ideal.

Use Free Draining Mixes

Soilless mixes work far better than standard potting soils. Opt for porous media like orchid bark, perlite, peat or sphagnum to avoid root rot.

Allow Drying Between Watering

Epiphyte roots rot easily if overwatered. Allow pots to dry out between waterings. Misting can supplement but is not enough alone.

Increase Humidity

Humidity should be 50-60% or higher. Group plants together, use pebble trays, run humidifiers, or grow epiphytes in terrariums to boost moisture.

Ensure Ample Airflow

Stagnant conditions encourage fungal and bacterial diseases. Use hanging pots and fans to keep air moving.

Fertilize Lightly

Epiphytes are adapted to low nutrient conditions. Use quarter strength liquid fertilizers every few weeks during growth periods.

Provide Support Structures

For climbing epiphytes, install trellises, plaques, poles or mounts made of natural materials to simulate host trees.

Mist Frequently

Many epiphytes appreciate occasional misting between regular waterings. Use room temperature distilled or rain water to mitigate plant stress.

With proper care replicating their natural conditions, cultivated epiphytes can thrive while bringing lush tropical vibes indoors!

Fascinating Epiphytes

The diversity of the epiphytic lifestyle has produced many plants with amazing and unusual adaptations:

Strangler Figs

These fascinating Ficus begin life as epiphytes high in the canopy. They send long roots down to the forest floor that gradually enlarge and fuse, slowly engulfing and killing their host tree.

Rafflesia

This bizarre parasitic flowering plant, native to the rainforests of Indonesia, produces the world’s largest flower, reaching over 3 feet wide! It lacks leaves and stems, absorbing nutrients directly from its vine host.

Ecuadorian Hyacinth Orchid

A stunning but rare epiphytic orchid species equipped with large pseudobulbs that store water during the dry season. Two attendant wasp species are the only pollinators capable of reaching the nectar spur.

Wilkiea huegeliana

A unique epiphytic gymnosperm species and the sole member of the ancient family Podocarpaceae that has adapted to life off the forest floor. This rare “orchid conifer” grows only on a single mountaintop in Australia.

Pygmy Drosera

These tiny carnivorous sundews have evolved an epiphytic lifestyle to gain access to canopy insects. Sticky traps on their wiry leaves catch prey to supplement the poor nutrient conditions high in the trees.

Miltonia Orchid

Also known as “Pansy Orchids”, many of these beautifully patterned epiphytes originate from cool, high-elevation cloud forests. Long flower spikes emerge from the base of strap-like pseudobulbs.

Tillandsia airplants

One of the most specialized of all epiphyte groups, with over 650 species relying solely on trichomes for foliar uptake of water and nutrients. Many also change color based on light intensity and moisture conditions.

Platycerium ferns

Bifurcated fronds and fuzzy stomata on the upper surfaces characterize these uniquely shaped epiphytic ferns. Two distinct life stages occur as sporelings establish on the fern itself and gradually take over.

The great diversity and microscale complexity of epiphyte communities continues to captivate biologists and plant enthusiasts alike! Their intricate ecologies illuminate just how integrated and interdependent forest ecosystems truly are.

Conclusion

Epiphytes represent a diverse array of plant families that have converged evolutionarily on strategies allowing them to colonize tree canopies. While often overlooked compared to more showy flowers, epiphytes are integral components of healthy tropical and temperate forests worldwide. Their unique adaptations allow them to efficiently cycle water and nutrients high up in the canopy despite rootless, suspended conditions. Unfortunately, deforestation, climate change and other threats are putting these sensitive ecological communities at risk. Scientific study and directed conservation efforts focused on preserving primary forest habitats can ensure epiphytes continue prospering, clinging tenaciously to bough and branch as they have done for millennia. With an appreciation for how complex and interconnected rainforests are, we can better safeguard these critical ecosystems and all the fascinating flora and fauna that call them home.