Epiphytes
Description & Overview
Epiphytes, specifically vascular epiphytes, are those plants that germinate and take root on other plants. These plants generally exhibit commensal relationships with their host plants, and therefore epiphytes receive shelter and protection with no cost or benefit to their host plant [2]. Epiphytes can be both obligate and facultative [3]. Facultative epiphytes are plant species that grow terrestrially and epiphytically approximately the same amount of times across their distribution. If a species grows epiphytically at least 95 percent of the time, it is considered an obligate epiphyte [4]. Plants that grow on other plants for only a portion of their life are referred to as "hemi-epiphytes" [5]. Additionally "accidental epiphytes" can occur when a plant that does not usually grow epiphytically at any point in its life cycle does so due to a need or opportunity for resources [3]. Epiphytes account for approximately 10 percent of all plant diversity. It is estimated that over 24,000 vascular plants are considered to be epiphytes, and they are most commonly concentrated in tropical areas where they provide significant ecosystem services [5]. Since epiphytes usually have no direct contact with soil, their most common threat is desiccation, thus these plants have many unique adaptations that allow them to conserve water and thrive [6].
Ecology & Evolution
Ecologically, epiphytes exhibit opportunism, filling gaps in an ecosystem and often growing in tree crowns. Most vascular plants can display epiphytic growth if they are in the correct conditions. For example, the aforementioned "accidental epiphytes" result from a species taking advantage of beneficial conditions in its microhabitat. In these cases, a plant species may have a fundamental niche in which it can grow epiphytically but is usually not able to due to competition or lack of resources [4].
Therefore, evolutionarily, epiphytism has resulted from plants adapting to canopy conditions and taking advantage of empty space [4]. Epiphytism and its traits is also thought to have led to rapid diversification in certain plant families. For example, approximately 75 percent of the family Orchidaceae and 59 percent of the family Bromeliaceae are epiphytic, showing that this growth style has been significant and beneficial in these species' life histories [7].
Epiphytes thus have many unique adaptations in their growth that help them to thrive in their environment and to retain ecosystem stability. For instance, epiphyte habitats are usually considered to be discontinuous, and because of their common habitat in canopies, this means that their seeds are usually dispersed via wind or birds. Additionally, these plants require roots that are specially designed to grow in areas that do not contain soil. This unique growth system also means that epiphytes need to be well-adapted to absorbing rainwater, as they cannot access water through soil. Epiphytes also have to be smaller and lighter in size and weight in order to not pressure the plant they grow on and cause stress or possible dislodgement. Along with this, epiphytes need to have leaves adapted to light conditions of canopies and a structure that is able to retain water in times of stress [8].
Epiphytes & Soil
Though epiphytic plants do not directly contact it, they do have indirect effects on the soil of their microclimates. Soils beneath epiphyte host plants tend to absorb less water from rainfall and fog. Especially during wet seasons, epiphytes have a strong influence on the amount of water from precipitation retained by soil [9].
Common Vascular Epiphytes
Orchids
The orchid family (Orchidaceae) is one of incredible diversity. Across all orchids, though, with their variety of shapes, sizes, and growth strategies, they each have six waxy or velvety "petal-like parts" [10]. These plants can either grow terrestrially or epiphytically (relying on trees for this growth). Precipitation and water levels typically determine if orchids will grow epiphtically, and warmer temperatures often correlate to epiphytic growth in orchids. Therefore, they tend to display this growth strategy in the humid climate of tropical areas. When orchids display epiphytic growth, their leaves tend to become thick and their aerial roots become covered in a layer of dead skin cells. These adaptations help the plant to better conserve and absorb water. Other adaptations of epiphytic orchids include having pseudobulbs that help retain water and practicing Crassulacean Acid Metabolism (CAM) photosynthesis [11].
Bromeliads
The bromeliad family (Bromeliaceae) contains about 2,500 species of which about half are epiphytes. These plants are native to the tropical areas of North and South America. Typically, bromeliads are stemless, and they display a rosette of leaves [12]. Out of all epiphytes, bromeliads are thought to be uniquely significant in their ecosystems. For instance, some bromeliads have overlapping leaves that provide areas of shelter for small animals. Additionally, bromeliads have reservoirs that store water, and the evaporation of water from this area can affect the behavior of tree species. Bromeliads provide nectar, flowers, and fruit for many animals as well. These plants absorb nutrients through both roots and aerial parts [13].
Ferns
Ferns are one of Earth's oldest plant groups, and today this group has approximately 10,500 species, with its diversity only outnumbered by flowering plants [14]. About 29 percent of ferns are epiphytic, and this growth style for ferns dates back to the Cretaceous period [6]. Therefore, the fern gametophyte and sporophyte forms have adapted to this lifestyle. For example, epiphytic fern gametophytes are observed to have more dissection and branching in their morphology as compared to terrestrial fern gametophytes. This is useful in reproduction for epiphytic ferns, as they can grow and branch out far enough in order to reach another fern, rather than undergoing self-fertilization [14].
The fern family Polypodiaceae has unique adaptations that allow its species to thrive epiphytically. One such adaptation is poikilohydry, which allows these plants to survive and recover from significant periods of dehydration. Additionally, species in this family have specialized methods that allow them to collect humus as an alternative way to obtain nutrients [6].
References
[3] [5] [4] [7] [8] [11] [13] [12] [10] [14] [6] [9] [2] [1]
- ↑ Jump up to: 1.0 1.1 1.2 1.3 1.4 1.5 iNaturalist. https://www.inaturalist.org/.
- ↑ Jump up to: 2.0 2.1 Naranjo, C., Iriondo, J., Riofrio, M., Lara-Romero, C.. (2019). "Evaluating the structure of commensalistic epiphyte–phorophyte networks: a comparative perspective of biotic interactions" AoB PLANTS. 11(2): plz011. https://doi.org/10.1093/aobpla/plz011.
- ↑ Jump up to: 3.0 3.1 3.2 Zotz, Gerhard. (12 Nov 2012). "The systematic distribution of vascular epiphytes – a critical update." Botanical Journal of the Linnean Society. The Linnean Society of London. 171: 453–481. https://academic.oup.com/botlinnean/article/171/3/453/2416203.
- ↑ Jump up to: 4.0 4.1 4.2 4.3 Hoeber, V. and Zotz, G.. (15 Mar 2022). "Accidental epiphytes: Ecological insights and evolutionary implications." Ecological Monographs. The Ecological Society of America. 92(4): e1527. https://doi.org/10.1002/ecm.1527.
- ↑ Jump up to: 5.0 5.1 5.2 Nieder, J., Prosperi, J., Michaloud, G.. (2001). "Epiphytes and their contribution to canopy diveristy." Plant Ecology. Kluwer Academic Publishers. 153: 51-63. https://www.researchgate.net/publication/226617674_Epiphytes_and_their_contribution_to_canopy_diversity.
- ↑ Jump up to: 6.0 6.1 6.2 6.3 Dubuisson, J., Schneider, H., Hennequin, S.. (2009). "Epiphytism in ferns: diversity and history." C.R. Biologies. 332: 120-128. http://dx.doi.org/10.1016/j.crvi.2008.08.018.
- ↑ Jump up to: 7.0 7.1 Taylor, A., Zotz G., Weigelt P., Cai L.,Karger D. N., König C., & Kreft H. (2022). "Vascular epiphytes contribute disproportionately to global centres of plant diversity." Global Ecology and Biogeography, 31: 62–74. https://doi.org/10.1111/geb.13411.
- ↑ Jump up to: 8.0 8.1 Hietz, P., Wagner, K., Nunes Ramos, F.,Cabral, J. S., Agudelo, C., Benavides, A. M., Cach-Pérez, M. J.,Cardelús, C. L., Chilpa Galván, N., Erickson Nascimento daCosta, L., de Paula Oliveira, R., Einzmann, H. J. R., de PaivaFarias, R., Guzmán Jacob, V., Kattge, J., Kessler, M., Kirby, C.,Kreft, H., Krömer, T., … Zotz, G. (2022). "Putting vascular epiphytes on the traits map." Journal of Ecology, 110: 340–358. https://doi.org/10.1111/1365-2745.13802.
- ↑ Jump up to: 9.0 9.1 Stanton, D., Huallpa Chávez, J., Villegas, L., Villasante, F., Armesto, J., Hedin, L., and Horn, H.. (2014). "Epiphytes improve host plant water use by microenvironment modification." Functional Ecology. British Ecological Society. 28: 1274-1283. https://doi.org/10.1111/1365-2435.12249.
- ↑ Jump up to: 10.0 10.1 University of Wisonsin-Madison. (5 Nov 2010). "Orchids." Wisconsin Horticulture. University of Wisconsin-Madison. https://hort.extension.wisc.edu/articles/orchids/.
- ↑ Jump up to: 11.0 11.1 Taylor, A., Keppel, G., Weigelt, P., Zotz, G., Kreft, H.. (2021). "Functional traits are key to understanding orchid diversity on islands." Ecography. 44: 703–714. http://dx.doi.org/10.1111/ecog.05410.
- ↑ Jump up to: 12.0 12.1 University of Wisconsin-Madison. (2025). "Bromeliads." Wisconsin Horticulture. University of Wisconsin-Madison. https://hort.extension.wisc.edu/articles/bromeliads/.
- ↑ Jump up to: 13.0 13.1 Nievola, C., Kanashiro, S., Tamaki, V., Guardia, M., Suzuki, R., Costa, J., Baptista, W., Cachenco, M., Shidomi, Y., Santos Junior, N.. (2022). "Simultaneous relocation strategy of bromeliads as epiphytes or terricolous in the Montane Dense Ombrophilous Forest of Parque Estadual da Cantareira, São Paulo State, Brazil." Hoehnea 49: e052022. http://dx.doi.org/10.1590/2236-8906-05-2022
- ↑ Jump up to: 14.0 14.1 14.2 Pinson, Jerald. (2021). "About Ferns." American Fern Society. https://www.amerfernsoc.org/about-ferns.