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.
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]
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.
These specialized aerial roots enable plants to breathe air in habitats with waterlogged soil. The roots may grow downward from the stem or upward from typical roots. Some botanists classify them as aerating roots rather than aerial roots if they emerge from the soil. The surface of these roots is covered with porous lenticels, which lead to air-filled spongy tissue called aerenchyma. This tissue facilitates the diffusion of gases throughout the plant, as oxygen diffusion coefficient in air is four orders of magnitude greater than in water. [2]
Pneumatophores differentiate the black mangrove and grey mangrove from other mangrove species. Fishers in some areas of Southeast Asia make corks for fishing nets by shaping the pneumatophores of mangrove apples ( Sonneratia caseolaris ) into small floats. [3]
Members of the subfamily Taxodioideae produce woody above-ground structures, known as cypress knees, that project upward from their horizontal roots. One hypothesis suggests that these structures function as pneumatophores, facilitating gas exchange in waterlogged soils. However, modern research has largely discredited this idea, as the knees lack aerenchyma and gas exchange through them is not significant. Their true functions remain unclear, with alternative theories proposing roles such as nutrient acquisition or storage, structural support, or erosion prevention. [4]
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.
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 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) [5] 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. [6]
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 Philodendron 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. [7] 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.
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.
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. In some cases, a rainforest tree's epiphytes may total "several tonnes". 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.
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.
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 a "strangler fig" because like many other trees in the genus Ficus it starts out as epiphyte, that is, leaning on another tree that it ends up suffocating.
Coleoptile is the pointed protective sheath covering the emerging shoot in monocotyledons such as grasses in which few leaf primordia and shoot apex of monocot embryo remain enclosed. The coleoptile protects the first leaf as well as the growing stem in seedlings and eventually, allows the first leaf to emerge. Coleoptiles have two vascular bundles, one on either side. Unlike the flag leaves rolled up within, the pre-emergent coleoptile does not accumulate significant protochlorophyll or carotenoids, and so it is generally very pale. Some preemergent coleoptiles do, however, accumulate purple anthocyanin pigments.
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. Its small fruit are favored by some birds. Ficus tree has shown to have environmental benefits in urban areas like being a biomonitor. The plant also has allergens associated with it.
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.
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.
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.
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.
In natural science, subaerial has been used since 1833, notably in geology and botany, to describe features and events occurring or formed 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 is a heritage-listed tree at Curtain Fig Tree Road, East Barron near 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.
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.
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.
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.
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.
Important structures in plant development are buds, shoots, roots, leaves, and flowers; plants produce these tissues and structures throughout their life from meristems located at the tips of organs, or between mature tissues. Thus, a living plant always has embryonic tissues. By contrast, an animal embryo will very early produce all of the body parts that it will ever have in its life. When the animal is born, it has all its body parts and from that point will only grow larger and more mature. However, both plants and animals pass through a phylotypic stage that evolved independently and that causes a developmental constraint limiting morphological diversification.
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.
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.
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. According to E.J.H. Corner, if this fig germinates in a boulder field its roots can extend "extraordinary distances, up to several hundred feet" over and between the rocks.