Epiphyte

Epiphytes are plants or plant-like organisms that grow upon the surface of other plants, deriving moisture and nutrients from the air, rain, mist or from organic debris accumulated around them. The host plant, known as the phorophyte, provides only physical support and is not ordinarily harmed by the presence of epiphytes, distinguishing the relationship from parasitism. Epiphytes form a vital component of many terrestrial and marine ecosystems, contributing significantly to biodiversity, nutrient cycling and habitat complexity.
Found across a vast range of climates—from temperate forests to humid tropical rainforests and marine coastal environments—epiphytes include flowering plants, ferns, mosses, lichens, algae and numerous invertebrate groups in marine systems. Their unique adaptations allow them to occupy ecological niches high above the ground or fixed to submerged vegetation, creating microhabitats essential for many organisms.

Distribution and Ecological Importance

Epiphytes are especially prominent in tropical rainforests, where moisture and light conditions in the canopy allow large assemblages to develop. In some rainforest trees the combined biomass of epiphytes can reach several tonnes. Mosses, liverworts, lichens and algae dominate epiphytic communities in temperate zones, while in the tropics flowering plants, ferns and bromeliads become more abundant.
These organisms play an essential role in nutrient cycling. They intercept and store water, capture airborne nutrients and support a variety of organisms, including frogs, insects, spiders, fungi and bacteria. Many canopy-dwelling animals depend directly on epiphytes for refuge, moisture or breeding sites. Older branches tend to support a richer epiphytic flora because they accumulate more debris, humidity and surface irregularities.
Epiphytes influence the microenvironment of forest canopies. By retaining water, they keep canopy conditions cooler and more humid, which can reduce transpiration rates in the host plant. Some nonvascular epiphytes such as mosses and lichens are particularly noted for their rapid water uptake, enabling them to survive fluctuating moisture regimes.

Major Groups of Terrestrial Epiphytes

Epiphytes occur across nearly all major plant groups. Among terrestrial species:

• Flowering plants (Angiosperms) represent about 24,000 species, approximately 89 per cent of known terrestrial epiphytes. Many orchids and bromeliads belong to this group.
• Leptosporangiate ferns contribute roughly 2,800 species, accounting for 10 per cent of all terrestrial epiphytes.
• Clubmosses (Lycopodiaceae) include about 190 species.
• Additional epiphytic representatives occur within spikemosses, cycads, gnetophytes and other fern lineages.

Prominent examples include mosses, orchids, bromeliads such as Tillandsia (Spanish moss), and certain cacti like Rhipsalis and Epiphyllum. Epiphytic taxa were first systematically studied in the late nineteenth century, notably in the work of Andreas Franz Wilhelm Schimper, whose 1888 monograph established key ecological concepts in the field.
In Europe, although few vascular plants are obligate epiphytes, extensive communities of mosses and lichens thrive on tree trunks and branches in humid western coastal regions. Occasionally, canopy soils may accumulate in rot holes, allowing small shrubs or grasses to take root without contacting the ground.

Holoepiphytes and Hemiepiphytes

Epiphytes are commonly classified according to their life cycle in relation to the ground:

• Holoepiphytes spend their entire life cycle without rooting in the soil. Many orchids exemplify this category.
• Hemiepiphytes begin life as epiphytes but later establish contact with the ground when roots extend downward. Strangler figs are a well-known example.

This distinction highlights contrasting strategies for nutrient acquisition, water use and structural support.

Nutrient and Water Relations

Because epiphytes lack direct access to soil nutrients, they must rely on alternative sources. These include atmospheric water inputs such as fog, dew and rain, dissolved nutrients washed down from canopy surfaces, and the decomposition of accumulated organic matter. Some epiphytes host nitrogen-fixing microorganisms, contributing biologically available nitrogen to the canopy ecosystem.
By living high in the canopy, many epiphytes benefit from increased light availability compared with ground-dwelling herbs. Reduced herbivore pressure in elevated habitats may also offer additional advantages.
Epiphytic adaptations often include specialised structures such as absorptive leaf surfaces, water-holding tanks (as seen in many bromeliads), and physiological mechanisms that conserve water.

Plant Metabolism and Adaptations

A significant number of epiphytes have evolved crassulacean acid metabolism (CAM), a water-efficient photosynthetic pathway that allows plants to open stomata primarily at night to reduce water loss. It is estimated that about half of all epiphytic orchids use CAM. Other CAM epiphytes occur in the Bromeliaceae (e.g., Aechmea, Tillandsia), epiphytic cacti and certain Apocynaceae such as Hoya and Dischidia.
These adaptations reflect the challenges of intermittent water supply and high irradiance in canopy environments.

Marine Epiphytes

Marine epiphytes differ substantially from terrestrial forms. They include algae, bacteria, fungi, bryozoans, sponges, ascidians, protozoans, crustaceans and molluscs that colonise the surfaces of seagrasses or algae. Light, temperature, water movement and nutrient availability all influence settlement and growth patterns.
Photosynthetic algae are the most common marine epiphytes and can contribute between 20 and 60 per cent of an ecosystem’s total primary productivity. They form a key food source for numerous animals, including snails and nudibranchs, and their composition can indicate environmental conditions.
Increased nutrient input from agricultural runoff and urban stormwater has led to elevated epiphyte loads in some marine habitats. Excessive epiphytic growth can smother host plants such as seagrasses by blocking sunlight or nutrient access, leading to reduced growth or mortality.

Ecological Interactions and Environmental Indicators

Epiphytes can act as indicators of environmental change. Their sensitivity to humidity, atmospheric quality and nutrient levels allows scientists to use changes in epiphytic communities to assess ecosystem health, especially in forests and coastal environments. The rapid generation times of many marine epiphytes make them particularly responsive to short-term environmental fluctuations.

Broader Significance

Epiphytes enhance structural complexity in ecosystems, whether in tropical canopies or marine environments. They are essential components of overall biodiversity and play a central role in sustaining food webs, hydrological processes and nutrient cycles. Their wide distribution and exceptional adaptive strategies illustrate the flexibility and ingenuity of plant and plant-like organisms in occupying non-soil habitats.