Aerial root

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The Grey Mangrove (Avicennia marina)'s pneumatophorous aerial roots Pneumatophore overkill - grey mangrove.JPG
The Grey Mangrove ( Avicennia marina )'s pneumatophorous aerial roots
A Schefflera arboricola indoor bonsai soon after branch pruning to show extensive aerial roots. Schefflera bonsai 2 (1).jpg
A Schefflera 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 above the ground. They are almost always adventitious. 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 ( M. 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 are 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.

Fishermen in some areas of Southeast Asia make corks for fishing nets by shaping the pneumatophores of Sonneratia caseolaris (aka "Mangrove Apple") into small floats. [2]

Members of the subfamily Taxodioideae produce woody aboveground 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.

When the soil upon which a halophytic plant is growing is highly salicin and largely anaerobic soil, in order to aide in respiration, the plant shoots pneumatophores. It is important to mention that even in other plants the gaseous exchange which is done at leaves is of minimal work for roots which are a lot further away. Roots absorb their own, dissolved, oxygen from the soil. However, since saline soil is largely anaerobic it becomes impossible for the roots to do gaseous exchange through soil and hence form pneumatophores that can absorb oxygen directly from air.

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 a good example of this.

Propagative roots

Adventitious roots usually develop from plantlet nodes formed via horizontal, aboveground 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 envelop of the aerial roots, are actually totally water proof, 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 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. [3]

See also

Related Research Articles

Root Part of a 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 most often lie 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.

Epiphyte Non-parasitic organism that grows upon another plant but is not nourished by it

An epiphyte is an organism that grows on the surface of a plant and derives its moisture and nutrients from the air, rain, water or from debris accumulating around it. 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.

Banyan Subgenus of plants, the banyans

A banyan, also spelled "banian", is a fig that begins its 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 denominates 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.

Clonal colony

A clonal colony or genet is a group of genetically identical individuals, such as plants, fungi, or bacteria, that have grown in a given location, all originating vegetatively, not sexually, from a single ancestor. In plants, an individual in such a population is referred to as a ramet. In fungi, "individuals" typically refers to the visible fruiting bodies or mushrooms that develop from a common mycelium which, although spread over a large area, is otherwise hidden in the soil. Clonal colonies are common in many plant species. Although many plants reproduce sexually through the production of seed, reproduction occurs by underground stolons or rhizomes in some plants. Above ground, these plants most often appear to be distinct individuals, but underground they remain interconnected and are all clones of the same plant. However, it is not always easy to recognize a clonal colony especially if it spreads underground and is also sexually reproducing.

<i>Avicennia marina</i> Species of plant

Avicennia marina, commonly known as grey mangrove or white mangrove, is a species of mangrove tree classified in the plant family Acanthaceae. As with other mangroves, it occurs in the intertidal zones of estuarine areas.

<i>Avicennia germinans</i>

Avicennia germinans, the black mangrove, is a shrub or small tree to 12 meters (39') in the acanthus family, Acanthaceae. It grows in tropical and subtropical regions of the Americas, on both the Atlantic and Pacific Coasts, and on the Atlantic Coast of tropical Africa, where it thrives on the sandy and muddy shores where seawater reaches. It is common throughout coastal areas of Texas and Florida, and ranges as far north as southern Louisiana and coastal Georgia in the United States.

In natural science, subaerial, has been used since 1833, notably in geology and botany, to describe events or features that are formed, located, or taking place immediately on or near the Earth's land surface. They are thus exposed to Earth's atmosphere. This may be contrasted with subaqueous events or features located below a water surface, submarine events or features located below a sea surface, subterranean events or features located below ground, or subglacial events or features located below glacial ice such as ice sheets.

Curtain Fig Tree

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.

Basal shoot

Basal shoots, root sprouts, adventitious shoots, and suckers are words for various kinds of shoots that grow from adventitious buds on the base of a tree or shrub, or from adventitious buds on its roots. Shoots that grow from buds on the base of a tree or shrub are denominated "basal shoots"; these are distinguished from shoots that grow from adventitious buds on the roots of a tree or shrub, which are denominated "root sprouts". A plant that produces root sprouts is described as surculose. Although a product of adventitious buds on a plant, water sprouts are distinct from basal shoots and root sprouts. They are colloquially yet incorrectly denominated "suckers", which word colloquially denominates basal shoots and root sprouts. Water sprouts occur on the above ground stem, branches, or both of trees and shrubs, well above the base of the plant and its roots, where adventitious buds can produce basal shoots and root sprouts, respectively.

The Florida mangroves ecoregion, of the mangrove forest biome, comprise an ecosystem along the coasts of the Florida peninsula, and the Florida Keys.

Hemiepiphyte plants that spend part of their life cycle as epiphytes

A hemiepiphyte is a plant that spends part of its life cycle as an epiphyte. The seeds of primary hemiepiphytes germinate in the canopy and initially live epiphytically. They send roots downward, and these roots eventually make contact with the ground. Secondary epiphytes are root-climbers that begin as rooted vines growing upward from the forest floor, but later break their connection to the ground. When this happens, they may send down long roots to the ground.

<i>Ceratopteris thalictroides</i>

Ceratopteris thalictroides is a fern species belonging to the genus Ceratopteris, one of only two genera of the subfamily Parkerioideae of the family Pteridaceae.

<i>Metrosideros robusta</i>

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 umbellata</i>

Metrosideros umbellata, the southern rata, is a tree endemic to New Zealand. It grows up to 15 metres (49 ft) or more tall with a trunk up to 1 metre or more in diameter. It produces masses of red flowers in summer. Unlike its relative, northern rata, this species rarely grows as an epiphyte.

<i>Metrosideros fulgens</i>

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>

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 Mahia 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.

This page provides a glossary of plant morphology. Botanists and other biologists who study plant morphology use a number of different terms to classify and identify plant organs and parts that can be observed using no more than a handheld magnifying lens. This page provides help in understanding the numerous other pages describing plants by their various taxa. The accompanying page—Plant morphology—provides an overview of the science of the external form of plants. There is also an alphabetical list: Glossary of botanical terms. In contrast, this page deals with botanical terms in a systematic manner, with some illustrations, and organized by plant anatomy and function in plant physiology.

New Guinea mangroves A mangrove ecoregion that covers extensive areas of the coastline New Guinea

The New Guinea mangroves is a mangrove ecoregion that covers extensive areas of the coastline New Guinea, the large island in the western Pacific Ocean north of Australia.

<i>Sonneratia caseolaris</i>

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>Bruguiera cylindrica</i>

Bruguiera cylindrica is a mangrove in the family Rhizophoraceae. It grows in mangrove swamps in tropical Asia.

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. 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.