Aerial root

Last updated
The grey mangrove (Avicennia marina)'s pneumatophorous aerial roots Pneumatophore overkill - grey mangrove.JPG
The grey mangrove ( Avicennia marina )'s pneumatophorous aerial roots
A Heptapleurum arboricola indoor bonsai soon after branch pruning to show extensive aerial roots. Schefflera bonsai 2 (1).jpg
A Heptapleurum arboricola indoor bonsai soon after branch pruning to show extensive aerial roots.
Banyan tree of undetermined species in Fort Myers, Florida Banyan tree Old Lee County Courthouse.jpg
Banyan tree of undetermined species in Fort Myers, Florida
European beech with aerial roots in a wet Scottish Glen. Beech Aerial Roots.JPG
European beech with aerial roots in a wet Scottish Glen.
Hybrid elm cultivar with aerial roots, Edinburgh Ulmus (unknown cultivar). Royal Terrace, Edinburgh (5).jpg
Hybrid elm cultivar with aerial roots, Edinburgh
Indian banyan tree in Kodungallur Temple, Kerala, India Ficus benghalensis @ Kodungallur India 01.jpg
Indian banyan tree in Kodungallur Temple, Kerala, India

Aerial roots are roots growing above the ground. They are often adventitious, i.e. formed from nonroot tissue. They are found in diverse plant species, including epiphytes such as orchids ( Orchidaceae ), tropical coastal swamp trees such as mangroves, banyan figs ( Ficus subg. Urostigma ), the warm-temperate rainforest rata ( Metrosideros robusta ), and pohutukawa trees of New Zealand ( Metrosideros excelsa ). Vines such as common ivy ( Hedera helix ) and poison ivy ( Toxicodendron radicans ) also have aerial roots.

Contents

Types of aerial roots

This plant organ that is found in so many diverse plant-families has different specializations that suit the plant-habitat. In general growth-form, they can be technically classed as negatively gravitropic (grows up and away from the ground) or positively gravitropic (grows down toward the ground). [1]

"Stranglers" (prop-root)

Banyan trees are an example of a strangler fig that begins life as an epiphyte in the crown of another tree. Their roots grow down and around the stem of the host, their growth accelerating once the ground has been reached. Over time, the roots coalesce to form a pseudotrunk, which may give the appearance that it is strangling the host.

Another strangler that begins life as an epiphyte is the Moreton Bay fig (Ficus macrophylla) of tropical and subtropical eastern Australia, which has powerfully descending aerial roots. In the subtropical to warm-temperate rainforests of northern New Zealand, Metrosideros robusta , the rata tree, sends aerial roots down several sides of the trunk of the host. From these descending roots, horizontal roots grow out to girdle the trunk and fuse with the descending roots. In some cases, the "strangler" outlives the host tree, leaving as its only trace a hollow core in the massive pseudotrunk of the rata.

Pneumatophores

These specialized aerial roots enable plants to breathe air in habitats that have waterlogged soil. The roots may grow down from the stem, or up from typical roots. Some botanists classify these as aerating roots rather than aerial roots, if they come up from soil. The surface of these roots is covered with lenticel (small pores) which take up air into spongy tissue, which in turn uses osmotic pathways to spread oxygen throughout the plant as needed. Pneumatophores differentiate the black mangrove and grey mangrove from other mangrove species.

Pneumatophores of mangrove plant Pneumatophores of mangrove plant.jpg
Pneumatophores of mangrove plant

Fishers in some areas of Southeast Asia make corks for fishing nets by shaping the pneumatophores of mangrove apples ( Sonneratia caseolaris ) into small floats. [2]

Members of the subfamily Taxodioideae produce woody above ground structures, known as cypress knees, that project upward from their roots. These structures were initially thought[ by whom? ] to function as pneumatophores, but recent experiments have failed to find evidence for this hypothesis.

Haustorial roots

These roots are found in parasitic plants, where aerial roots become cemented to the host plant via a sticky attachment disc before intruding into the tissues of the host. Mistletoe is an example of this.

Propagative roots

Adventitious roots usually develop from plantlet nodes formed via horizontal, above ground stems, termed stolons, e.g., strawberry runners, and spider plant.

Some leaves develop adventitious buds, which then form adventitious roots, e.g. piggyback plant ( Tolmiea menziesii ) and mother-of-thousands ( Kalanchoe daigremontiana ). The adventitious plantlets then drop off the parent plant and develop as separate clones of the parent.

Aerial root pumping and physiology

Aerial roots may receive water and nutrient intake from the air. There are many types of aerial roots; some, such as mangrove, are used for aeration and not for water absorption. In other cases, they are used mainly for structure, and in order to reach the surface. Many plants rely on the leaf system for gathering the water into pockets, or onto scales. These roots function as terrestrial roots do.

Most aerial roots directly absorb the moisture from fog or humid air.

Some surprising results in studies on aerial roots of orchids show that the velamen (the white spongy envelope of the aerial roots), are actually totally waterproof, preventing water loss but not allowing any water in. Once reaching and touching a surface, the velamen is not produced in the contact area, allowing the root to absorb water like terrestrial roots.

Many other epiphytes - non-parasitic or semi-parasitic plants living on the surface of other plants - have developed cups and scales that gather rainwater or dew. The aerial roots in this case work as regular surface roots. There are also several types of roots, creating a cushion where a high humidity is retained.

Some of the aerial roots, especially in the genus Tillandsia , have a physiology that collects water from humidity, and absorbs it directly.

In the Sierra Mixe (named after the geographical area) [3] variety of maize, aerial roots produce a sweet mucus that supports nitrogen fixing bacteria, which supply 30–80 percent of the plant's nitrogen needs. [4]

Aerial roots on houseplants

Many plants that are commonly grown indoors can develop aerial roots, such as Monstera deliciosa, Pothos (Epipremnum aureum), Rubber Tree (Ficus elastica), Fiddle Leaf Fig (Ficus lyrata), Thaumatophyllum bipinnatifidum, many 'xPhilodendron and succulents such as Echeveria.

Aerial roots on houseplants do not serve as much of a purpose as on outdoor plants, as there is no rain indoors and indoor humidity is often low due to A/C and heating systems. However, studies have shown that increasing indoor humidity can result in houseplant aerial roots growing longer in length, resulting in lower levels of transpiration and more efficient intake of nitrogen than aroid houseplants grown in standard indoor humidity. [5] Aerial roots on houseplant cuttings increase the chances of successful propagation.

The presence of aerial roots is not an indicator of plant health. If a plant does not have aerial roots, that is no reason for concern.

See also

Related Research Articles

<span class="mw-page-title-main">Root</span> Basal organ of a vascular plant

In vascular plants, the roots are the organs of a plant that are modified to provide anchorage for the plant and take in water and nutrients into the plant body, which allows plants to grow taller and faster. They are most often below the surface of the soil, but roots can also be aerial or aerating, that is, growing up above the ground or especially above water.

<span class="mw-page-title-main">Epiphyte</span> Non-parasitic surface organism that grows upon another plant but is not nourished by it

An epiphyte is a plant or plant-like organism that grows on the surface of another plant and derives its moisture and nutrients from the air, rain, water or from debris accumulating around it. The plants on which epiphytes grow are called phorophytes. Epiphytes take part in nutrient cycles and add to both the diversity and biomass of the ecosystem in which they occur, like any other organism. They are an important source of food for many species. Typically, the older parts of a plant will have more epiphytes growing on them. Epiphytes differ from parasites in that they grow on other plants for physical support and do not necessarily affect the host negatively. An organism that grows on another organism that is not a plant may be called an epibiont. Epiphytes are usually found in the temperate zone or in the tropics. Epiphyte species make good houseplants due to their minimal water and soil requirements. Epiphytes provide a rich and diverse habitat for other organisms including animals, fungi, bacteria, and myxomycetes.

<span class="mw-page-title-main">Banyan</span> Subgenus of plants, the banyans

A banyan, also spelled banian, is a fig that develops accessory trunks from adjacent prop roots, allowing the tree to spread outwards indefinitely. This distinguishes banyans from other trees with a strangler habit that begin life as an epiphyte, i.e. a plant that grows on another plant, when its seed germinates in a crack or crevice of a host tree or edifice. "Banyan" often specifically denotes Ficus benghalensis, which is the national tree of India, though the name has also been generalized to denominate all figs that share a common life cycle and used systematically in taxonomy to denominate the subgenus Urostigma.

<i>Ficus benghalensis</i> Species of fig tree

Ficus benghalensis, or Ficus indica commonly known as the banyan, banyan fig and Indian banyan, is a tree native to the Indian Subcontinent. Specimens in India are among the largest trees in the world by canopy coverage. It is also known as the "strangler fig" because it starts out as epiphyte, that is, leaning on another tree that it ends up suffocating.

<i>Ficus benjamina</i> Species of fig

Ficus benjamina, commonly known as weeping fig, benjamin fig or ficus tree, and often sold in stores as just ficus, is a species of flowering plant in the family Moraceae, native to Asia and Australia. It is the official tree of Bangkok. The species is also naturalized in the West Indies and in the states of Florida and Arizona in the United States. It is one of the most common trees in Israeli cities and parks. In its native range, its small fruit are favored by some birds.

<span class="mw-page-title-main">Houseplant</span> Ornamental plant in a home or office

A houseplant, sometimes known as a pot plant, potted plant, or an indoor plant, is an ornamental plant that is grown indoors. As such, they are found in places like residences and offices, mainly for decorative purposes. Common houseplants are usually tropical or semi-tropical, and are often epiphytes, succulents or cacti.

<i>Ficus microcarpa</i> Species of fig

Ficus microcarpa, also known as Chinese banyan, Malayan banyan, Indian laurel, curtain fig, or gajumaru (ガジュマル), is a tree in the fig family Moraceae. It is native in a range from China through tropical Asia and the Caroline Islands to Australia. It is widely planted as a shade tree and frequently misidentified as F. retusa or as F. nitida.

<span class="mw-page-title-main">Strangler fig</span> Index of plants with the same common name

Strangler fig is the common name for a number of tropical and subtropical plant species in the genus Ficus, including those that are commonly known as banyans.

<i>Ficus citrifolia</i> Species of fig native to the Americas

Ficus citrifolia, also known as the shortleaf fig, giant bearded fig, Jagüey, wild banyantree and Wimba tree, is a species of banyan native to southern Florida, the Caribbean, Mexico, Central America, and northern South America south to Paraguay. It is distinguished from the closely related Florida strangler fig mainly by the finer veining in the leaves.

<i>Ficus elastica</i> Species of banyan tree

Ficus elastica, the rubber fig, rubber bush, rubber tree, rubber plant, or Indian rubber bush, Indian rubber tree, is a species of flowering plant in the family Moraceae, native to eastern parts of South and Southeast Asia. It has become naturalized in Sri Lanka, the West Indies, and the US state of Florida. Despite its common names, it is not used in the commercial production of natural rubber.

<span class="mw-page-title-main">Curtain Fig Tree</span> Heritage-listed tree in Queensland, Australia

Curtain Fig Tree is a heritage-listed tree at Curtain Fig Tree Road, Yungaburra, Tablelands Region, Queensland, Australia. It is one of the largest trees in Tropical North Queensland, Australia, and one of the best known attractions on the Atherton Tableland. It was added to the Queensland Heritage Register on 3 December 2009.

<i>Ficus pumila</i> Species of climbing fig

Ficus pumila, commonly known as the creeping fig or climbing fig, is a species of flowering plant in the mulberry family, native to East Asia and naturalized in parts of the southeastern and south-central United States. It is also found in cultivation as a houseplant. The Latin specific epithet pumila means "dwarf", and refers to the very small leaves of the plant.

<i>Metrosideros robusta</i> Species of epiphyte

Metrosideros robusta, the northern rātā, is a forest tree endemic to New Zealand. It grows up to 25 metres (82 ft) or taller, and usually begins its life as a hemiepiphyte high in the branches of a mature forest tree; over centuries the young tree sends descending and girdling roots down and around the trunk of its host, eventually forming a massive, frequently hollow pseudotrunk composed of fused roots. In disturbed ground, or where there are gaps in the forest cover, northern rātā will grow on the ground with a normal but short trunk.

<i>Metrosideros fulgens</i> Species of vine

Metrosideros fulgens is a forest liana or vine endemic to New Zealand. It occurs in coastal and lowland forest throughout the North Island, on the west coast of the South Island and on the Three Kings Islands north of Cape Reinga. It is one of a number of New Zealand Metrosideros species which live out their lives as vines, unlike the northern rata (M.robusta), which generally begins as a hemi-epiphyte and grows into a huge tree. Scarlet rātā is one of the better-known species of rātā vines, because it flowers in autumn or winter, and is often highly visible on well-lit host trees along forest roads, with vibrant displays of large red flowers that rise above the forest canopy.

<i>Metrosideros carminea</i> Species of vine

Metrosideros carminea is a forest liane or vine that is endemic to New Zealand. It occurs in coastal and lowland forest from Te Paki in the north of the North Island south to Māhia Peninsula and Taranaki. It is one of a number of New Zealand Metrosideros species which live out their lives as vines, unlike the northern rata (M.robusta), which generally begins as a hemi-epiphyte and grows into a huge tree.

<span class="mw-page-title-main">Indoor bonsai</span> Miniature tree cultivated indoors

Indoor bonsai are bonsai cultivated for the indoor environment. Traditionally, bonsai are temperate climate trees grown outdoors in containers. Tropical and sub-tropical tree species can be cultivated to grow and thrive indoors, with some suited to bonsai aesthetics shaped as traditional outdoor or wild bonsai.

<i>Ficus aurea</i> Species of strangler fig

Ficus aurea, commonly known as the Florida strangler fig, golden fig, or higuerón, is a tree in the family Moraceae that is native to the U.S. state of Florida, the northern and western Caribbean, southern Mexico and Central America south to Panama. The specific epithet aurea was applied by English botanist Thomas Nuttall who described the species in 1846.

<span class="mw-page-title-main">Balete tree</span> Several species of Filipino Ficus trees

The balete tree are several species of trees in the Philippines from the genus Ficus, which are broadly referred to as balete in the local language. A number of these are strangler figs, as they germinate upon other trees, before entrapping their host tree entirely and eventually killing it. Consequently the young plants are hemiepiphytes, i.e. epiphytes or air plants that grow several hanging roots which eventually touch the ground and take root. Some baletes produce natural rubber of an inferior quality. The Indian rubber tree, F. elastica, was formerly cultivated to some extent for rubber. Some of the species like tangisang-bayawak or Ficus variegata are large and could probably be utilized for match wood. The wood of Ficus species are soft, light, and of inferior quality, and the trees usually have ill-formed, short boles.

<i>Sonneratia caseolaris</i> Species of fruit and plant

Sonneratia caseolaris, commonly known as mangrove apple, is a species of plant in the family Lythraceae. The fruit is noted for its outward similarity to the persimmon fruit.

<i>Ficus superba</i> Species of epiphyte

Ficus superba, also known as sea fig or deciduous fig, is a hemiepiphytic tree of genus Ficus. It is one of the species known as banyans or "strangler figs" because of its potential to grow as a hemi-epiphyte and eventually progress to the strangling habit of species in this subgenus. It is, however, not an obligate hemi-epiphyte and can be found growing as single stemmed trees in forests. It is found in Japan, Taiwan, Australia, and China, as well as various parts of Southeast Asia, such as Thailand, Vietnam, Java, Kalimantan, the Lesser Sunda Islands, Moluccas, Seram Island, and Peninsular Malaysia.

References

  1. "UCLA Botany glossary page - Roots". Archived from the original on 2005-09-06. Retrieved 2005-10-10.
  2. "Berembang Sonneratia caseolaris". Wild Singapore. 2017-05-31. Retrieved 2019-04-12.
  3. Pskowski, Martha (July 16, 2019). "Indigenous Maize: Who Owns the Rights to Mexico's 'Wonder' Plant?". Yale E360.
  4. Daley, Jason (August 10, 2018). "The Corn of the Future Is Hundreds of Years Old and Makes Its Own Mucus". Smithsonian Magazine . ISSN   0037-7333.
  5. Sheeran, Laura; Rasmussen, Amanda (14 February 2023). "Aerial roots elevate indoor plant health: Physiological and morphological responses of three high-humidity adapted Araceae species to indoor humidity levels". Plant, Cell & Environment. 1 (12). doi: 10.1111/pce.14568 .