Root system generally involves two basic types of root systems, taproot and adventitious roots. These roots undergo various modifications, either naturally or under unfavorable conditions, which are essential for plant survival. Modified roots perform various physiological and mechanical functions which help the plant to thrive even in unsuitable conditions. Physiological modifications of roots help in food storage and respiration purposes, whereas mechanical functions help in the anchoring of plants. A detailed explanation for examples of modified roots is as follows.
Examples of modified tap roots
For food storage
1. Daucus carota
Daucus carota (Umbelliferae-Dicot) is the scientific name for carrot, a root vegetable. Carrots possess tap roots and these roots undergo several modifications for performing various functions like food storage. Carrot roots undergo modifications and form cone-like structures; therefore, are categorized under conical root modifications. These types of roots are thickest towards the base and gradually tapering towards the apex. The hypocotyl and the base of the stem after sloughing off the cortex become fleshy through the development of parenchyma in the phloem. Parenchyma is a simple permanent tissue that makes the storage tissue. The storage roots of this plant are usually swollen for the storage of various food materials.
Radish, also known as Raphanus sativus, is a Cruciferae- Dicot and an edible root vegetable belonging to the Brassicaceae family. Radish has a spindle-shaped structure, thickest from the middle and narrow from the ends, and is an example of fusiform tap root modification. The tapering/narrow ends include the base of the stem and the apex of the root. Xylem is the chief region for food storage but the storage also takes place outside the xylem region. Fleshy roots of radishes show a proliferation of parenchyma in the pith and the secondary xylem, accompanied by differentiation of concentric vascular bundles within this parenchyma. Radish is a rich source of antioxidants (calcium and potassium) and helps to lower high blood pressure levels and reduce the risk of heart diseases.
|Sub-species||R. raphanistrum sativus|
Its fusiform roots consist of swollen hypocotyl near the base and swollen taproot in the rest of the region. It is usually long and white color in appearance.
In European Radish, the taproot only forms the terminal tapering fleshy part of the root while the hypocotyl forms the middle fleshy parts. It is usually a short, red-colored taproot.
Brassica rapa, the scientific name of turnip, is a cruciferous vegetable that belongs to the Brassicaceae family. Turnips are also called top-shaped roots because of their structure and are categorized under napiform tap root modifications for food storage. The phloem and the cortex of turnip roots are narrow; therefore, food storage largely takes place in the xylem region. The massive swollen part of the turnip is the hypocotyl, while the taproots are present at the tapered/narrow end of the turnip. Various health benefits of turnip include-
- Help in lowering blood pressure
- Reduce the risk of cancer
- Help in weight loss
- Improves digestion
- Lowers the risk of intestinal problems
Beta Vulgaris or beetroot is a Chenopodiaceae-Dicot that belongs to the Amaranthaceae family. In beetroots, the alternate layers of the xylem and phloem leads to the formation of successive cambia. The secondary tissues of these roots accumulate starch in various parenchymatous and sclerenchymatous cells of the xylem and the phloem. Both the hypocotyl and roots of beet form swollen structure which helps to store food, starch, and water. Beetroot has a top-shaped structure and is an example of napiform taproot modification. Beetroots are rich in folate (vitamin B-9) which helps in cell growth and functioning. Folate helps to control the damage of blood vessels, thus reducing the risk of heart attack and stroke. Beetroot is also a rich source of diverse minerals such as potassium, sodium, phosphorous, calcium, magnesium, copper, iron, zinc, and manganese.
5. Mirabilis Jalapa
Mirabilis Jalapa is commonly known as a four O’ clock plant because the flowers of this plant open up in the late afternoon to produce a strong, sweet-smelling fragrance throughout the night and gets closed again in the morning. It is a perennial, herbaceous, bushy plant which belongs to the Nyctaginaceae family and is mainly found in temperate zones. Tap roots undergo modifications to form tuberous roots for storage purposes. Tuberous roots are the modified lateral roots for nourishment storage to store food and minerals. Tuberous roots produced in mirabilis jalapa are swollen, which stores nourishment and helps them to perennate through dry and cold periods.
6. Trichosanthes (Vern. Parwal)
Trichosanthes dioca, also known as pointed gourd, is a tropical perennial cucurbit plant which belongs to the Cucurbitaceae family. In regions of India and Bangladesh, it is also known as parwal or palwal. Trichosanthes plant has tuberous roots which are the modifications of tap roots for storage purposes. Despite growing underground, largely in darkness, roots emerge to be very sensitive to light. This plant is cultivated mainly as a vegetable, and also the leaves of this plant are used for its antipyretic, diuretic, cardiotonic, laxative, and antiulcer effects.
7. Ruellia tuberosa
Ruellia tuberosa, commonly known as cracker plant/minnieroot, is a small biennial plant from the Acanthaceae family containing thick fusiform tuberous roots (storage roots). Fusiform tuberous roots are modified forms of tap roots developed for storage purposes. The storage roots of this plant get swollen and fleshy to store food and minerals and the fruits of this plant are 2-3 cm long spindle-shaped capsules. Ruellia tuberosa is traditionally used as a diuretic, antipyretic, analgesic, anti-hypertensive, anthelmintic, abortifacient, and as an emetic in various disorders like bladder disease, kidney disorder, bronchitis, gonorrhea, and syphilis.
Nodulated roots (tuberculate roots)
1. Pisum sativum (Pea)
Pisum sativum, commonly known as pea or garden pea, is a dicotyledon annual plant that is known worldwide for its edible seeds and is mainly found in temperate areas of all continents. Pea is a legume which possesses nodulated roots, these nodules contain Rhizobium bacteria that fix nitrogen into assimilated substances for the plant. Uses of pisum sativum include-
- Immature pods and seeds are used as green vegetables, either fresh or frozen
- It is used as green forage for grazing animals as in situ, hay, or as silage
- It is usually grown for its mature seed which itself has many uses
Chickpea (Cicer arietinum) is also known as Bengal gram and is widely grown for its nutritious seeds. It is one of the earliest cultivated legumes and is rich in fiber, proteins, and is also a good source of iron, phosphorous, and folic acid. In this plant, the nodule formation by mesorhizobium species allow legumes and rhizobia to form a symbiotic relationship. Nodules colonized by bacteria receive nutrients from plants, while rhizobia provides fixed atmospheric nitrogen and makes it available to plants.
Arachis hypogaea is the scientific name for groundnut or peanut and is cultivated mainly for its edible seeds. It is a legume and is native to tropical South America. The seeds of this plant are highly nutritious and are rich in proteins and fats. The plant and the rhizobia bacteria form a nodule structure which houses the bacteria and creates the most beneficial conditions for the bacteria to thrive. A nodule is a site where nitrogen fixation occurs. Seeds of groundnut can be consumed either raw, boiled, or roasted. The shells of groundnut are used for making particle boards or used as fuel or filler in the agriculture industry.
Other examples of leguminous plants having nodulated roots are fenugreek, soyabean, and parasponia; whereas, non-leguminous plants such as alder and barberry also contain nodulated modified roots for nitrogen fixation.
1. Black mangrove
Avicennia germinans, commonly known as black mangrove, is a shrub which can reach up to an average height of 15-20 metres and is mostly found in tropical and subtropical regions of America. These plants are tough as they survive in harsh conditions like muddy areas, saline water, and hot temperatures. Unlike other mangrove species, it does not grow on prop roots instead it possesses long horizontal roots with finger-like projections known as pneumatophores which help the plant to breathe even when submerged in saline water. These erect, pencil-shaped pneumatophores originate from underground which provides oxygen to underwater root systems.
2. Sonneratia species
Sonneratia species do not contain tap roots instead they are moored by radiating cable roots that are 25-30 cm deep underground. Strong and woody pneumatophores/breathing roots protrude above the surface of these radial roots which helps to facilitate the gaseous exchange. The pneumatophores of Sonneratia species can reach up to a height of 10 feet (3 metres), otherwise, most pneumatophores range only between 8 and 20 inches (20 and 50 cm). Pneumatophores of these species are used for making corks, fishing floats, and shoe heels. Some examples of sonneratia species containing pneumatophores are as follows.
Sonneratia alba is a mangrove that belongs to the Lythraceae family. The word ‘alba’ is derived from the Latin word meaning “white”. Sonneratia alba is locally known as white chippi and produces beautiful white flowers with a slight pink color at their base.
Sonneratia caseoloris, commonly called mangrove apple, is one of the native mangrove plant that can naturally grow in both saltwater and freshwater. This plant mainly contains four types of roots including cable root, pneumatophore, feeding root, and anchor root. The cortex layer of the pneumatophore root contains two types of parenchyma, the round parenchyma and the aerenchyma. The aerenchyma present in the pneumatophores of this plant helps in gaseous exchange for respiration.
3. Heritiera fomes
Heritiera fomes, commonly known as the Sundari tree, is a medium-sized evergreen tree that is mainly found in the Sundarban forest located in the southern part of Bangladesh with an average height of 15-25metres. The name Sunderban is derived from the dominance of the mangrove species, Heritiera fomes, locally known as the Sundari (beautiful) tree because of its elegance. It is one of the species of mangrove plant and the only Hertiera genus species producing pneumatophores. These negatively geotropic pneumatophores come out of the mud surface to access atmospheric oxygen. These pneumatophore roots are covered with small pores, through which oxygen can be absorbed and carbon dioxide can be released. The trunk of heritiera fomes develops buttress roots (flange-like extensions) which are triangular, thin but strong, and are the largest of all flange pneumatophores. The leaves, stems, and roots of this plant are of utmost medicinal importance as they are used by rural peoples for the treatment of gastrointestinal disorders, skin diseases, and hepatic disorders. The bark of this plant is used in the treatment of diabetes, goiter, and skin diseases.
4. Bald cypress
Taxodium distichum, also known as Bald cypress, is a slow-growing tree that can reach up to an average height of 35–120 feet and has a trunk diameter of 3–6 feet; therefore, commonly referred to as a giant. In this plant, pneumatophores grow from horizontal roots just below the surface and bulge upward from the ground or water. Since this plant mainly occurs in swampy areas it is thought that the main function of pneumatophores is to transport air to drowned roots underground, which might also help in plant anchoring. These plants are mainly valued for the rot-resistant heartwood of mature trees, so they have been widely used to make fence posts, doors, flooring, caskets, cabinetry, boats, etc.
Examples of Adventitious modified roots
For physiological functions
1. Sweet Potato
Ipomoea Batatas (sweet potato) is a ConvoIvulaceae-Dicot that belongs to the morning glory family, Convolvulaceae. They are an example of simple tuberous adventitious root modifications and do not possess any particular/definite shape. In this type of plant, food is stored in the xylem region to a large extent, but food in these species can also be stored outside the xylem area. A complicated type of anomalous secondary thickening is present in sweet potatoes and the root is either a pentarch or a hexarch in its primary state. The cortex is delimited/separated from the stelar region by a single-layered distinct endodermis. Normally developed but highly parenchymatous primary and secondary xylem develops anomalous cambia around individual vessels or vessel groups and produces phloem, rich in the parenchyma, with laticifers away from vessels and with tracheary elements towards them. Large amounts of storage parenchyma cells are developed forming modified tuberous adventitious roots; thus helping in the storage of water and food materials. Along with storage roots, they also contain reproductive roots which help them reproduce through vegetative propagation.
Turmeric (Curcuma longa) is a rhizomatous herbaceous perennial plant of the ginger family, Zingiberaceae which is native to tropical South Asia. It is a flowering plant and rhizomes of this species are used in cooking. Storage roots of turmeric are the modified adventitious roots commonly called nodulose roots, which are mainly found swollen at the apex or tips. These nodulose roots help turmeric to store food, water, and minerals which are necessary for the physiological functioning of the plant. Favorable conditions for their survival involve, temperatures between 20 and 30 °C (68 and 86 °F) and a considerable amount of annual rainfall. Benefits of turmeric include-
- Help in controlling diabetes
- Might prevent cancer
- It helps in lowering cholesterol levels
- Treat various skin conditions
- Beneficial for people suffering from depression
- Helps in controlling weight
- It may help to cure gastrointestinal conditions
3. Curcuma amada
Mango ginger is the common name for Curcuma amada which belongs to the Zingiberaceae family. Curcuma amada has nodulose roots storage roots which are modified adventitious roots for storing minerals, food, and water. These storage roots of Curcuma amada are generally found swollen from the tips due to the accumulation of food. Both turmeric and mango ginger belong to the same genus but the difference between them is that turmeric has rich yellow tissue, whereas mango ginger has a pale yellow core. Mango ginger is also known for its large-extent medicinal effects like antioxidant, antibacterial, antifungal, anti-inflammatory, platelet aggregation inhibitory effects, cytotoxicity, antiallergic, hypotriglyceridemic, brine-shrimp lethal effects, enterokinase inhibitory effects, CNS depressant, and analgesic activity.
Arrowroot, scientifically known as Maranta arundinacea, is a large perennial herb found mostly in rainforest habitats and belongs to the Marantaceae family. Arrorroots exhibit storage roots which are modified forms of adventitious roots, commonly known as nodulose roots. When the cluster of long cylindrical roots becomes swelled and enlarged from the tips forming nodules are called nodulose roots. These roots store food and water which are essential for the proper functioning of plant. Arrowroot is a root vegetable and an edible rhizome native to countries such as America and the West Indies. It is usually processed in powder form, commonly known as arrowroot flour. Arrowroot is popularly known for its culinary and medicinal uses, but a unique application of arrowroot is that it also holds great significance in the cosmetic industry.
Dahlia is the genus of bushy, herbaceous perennial plants native to Mexico and Central America. It contains fasciculated tuberous roots (modified form of adventitious roots) for food storage and for vegetative propagation. These fasciculated roots develop in clusters at the stem base and become thick and fleshy for food storage. Both the roots and flowers of dahlia are edible, but roots can be eaten either raw or cooked only after removing the peel/outer skin. Dahlia is used in various fields for distinct purposes such as in landscaping, in floristry as a cut flower, in the pharmaceutical industry, in the cosmetic industry, in the food industry, and as raw material for the extraction of dyes. The roots of this plant are rich in inulin starch, which can further be converted into a sweetening substance, fructose, for diabetic patients. Along with storage roots, they also contain reproductive roots which help them reproduce through vegetative propagation.
The asparagus plant, scientifically known as Asparagus Officinalis, is a perennial flowering plant that belongs to the Asparagaceae family. They contain modified fasciculated adventitious roots for food storage purposes. It is one of the most nutritionally balanced vegetables. It is a great source of nutrients (fiber, folate), vitamins (vitamins A, C, and K), and anti-oxidants. It is edible and possesses numerous health benefits like weight loss, improved digestion, ease of hangovers, healthy pregnancy outcomes, inflammatory relief, and alleviating high blood pressure.
Tapioca is a processed starch product extracted from the cassava root, a perennial shrub that is found throughout South America. It is rich in carbohydrates which enhances calorie intake. Apart from this, it does not provide any other nutritional food value in terms of proteins, fat, vitamins, and minerals. It is also used as a dietary staple in various countries like Africa, Asia, and America. These plants contain swollen fleshy roots called root tubers. These tubers possess buds that grow into leafy shoots. These shoots then get detached from their parent plant and are capable of forming a new plant whose genotype and phenotype are similar to that of the parent plant.
Yam, an ancient food plant, is generally cultivated for their edible starchy tubers and belongs to the family Dioscoreaceae. These are mostly found in the regions of Africa, Asia, and America. The roots of these plants contain adventitious buds which grow into leafy shoots to form new plants. They are a good source of fiber, potassium, manganese, copper, antioxidants, vitamin A, and vitamin C; therefore, they are edible. One must avoid consuming yams raw as the proteins found in raw yams might be toxic in nature and can cause illness. Various health benefits of yams include boosting brain health, reducing inflammation, and improving blood sugar levels.
Tinospora mainly consists of 34 species, and the most common species T.cordifolia and T.crispa are mostly found in tropical and sub-tropical parts of Asia, Africa, and Australia. The herbs of Tinospora are used in the treatment of colds, headaches, pharyngitis, fever, diarrhea, oral ulcer, digestive disorder, and rheumatoid arthritis. Tinospora cordifolia is widely employed by Indian Ayurveda for treating diabetes. The roots of such plants undergo vegetative propagation as they contain adventitious buds which develop leafy shoots to form a new plant.
10. Dalbergia sissoo
Dalbergia sissoo is a deciduous rosewood tree that belongs to the Fabaceae family. It is mainly found in the foothills of the Himalayas ranging from Afghanistan in the west to Bihar, India, in the east. The intact roots of such woody plants develop adventitious buds, which put out shoots to form new plants. This plant possesses various therapeutic effects and is used to treat sore throats, dysentery, syphilis, bronchitis, inflammations, infections, hernia, skin diseases, and gonorrhea. It grows up to 8 feet in girth and 100 feet in height in wet areas, while in dry areas it grows only 10-15 meters in height.
11. Orchid (Orchidaceae)
Orchids are the largest flowering plants available in various shapes, colors, and sizes which belong to the Orchidaceae family. Orchids have the ability to conserve water in their thick stems. They are found everywhere except the Antarctica region. For eg, orchids are found as an epiphyte on a branch of a mango tree. Orchids contain epiphytic or hygroscopic roots, which absorb water/moisture from the atmosphere for plant survival under unfavorable conditions.
Bromeliads can be both terrestrial and epiphytic bromeliads. Epiphytic bromeliads are the most common example of aerial roots belonging to the Bromeliaceae family. They store rainwater in their leaves by leaves overlapping. Water and nutrient uptake is done by the leaves using hair-like structures called trichomes. Aerial roots of epiphytic bromeliads are found at the base of the plant and are usually thin, brown, and some inches long.
For mechanical functions
1. Banyan Tree (Ficus benghalensis)
Ficus benghalensis is a scientific name for banyan trees and it belongs to the Moraceae family. These plants are toxic to humans and pets. All the parts of the plant contain a highly irritant sap and consumption of any part of the plant may cause throat irritation, drooling, and vomiting. It is mainly found in monsoons and rainforests and can reach a height of up to 30 meters. This plant develops prop roots for its mechanical functioning. The roots grow downwards, like lianas, as aerial roots on the branches to provide support to the plant. India has the largest giant banyan trees all over the world and the notable ones are, Thimmamma Marrimanu, Kabirvad, and The great banyan. These trees can reach a height of up to 30 meters, and spread laterally indefinitely.
2. Red Mangroves (Rhizophora mangle)
Red mangroves, scientifically known as Rhizophora mangle, are broad-leaved evergreen trees that are easily remarkable with their above-ground prop roots and viviparous seeds. Red mangroves belong to the Rhizophoraceae family. Red mangroves are sometimes also called “walking trees” because their continuously growing prop roots make them look like they are walking on water. These prop roots develop to help hold the tree steady in its soft, muddy environment. In tropical regions, they can grow up to 80 feet in height. Red mangroves have edible fruits, but they are bitter in taste.
Pandanus is the scientific name of screwpine and it belongs to the Pandanaceae family. They are capable of reaching 60 feet but are found only 20-30 feet in height. Screwpines are found mostly in Asia, Africa, and Oceania. The stem of sugarcane contains supporting roots in their lower nodes, called stilt roots. These roots are used to enhance mechanical stability and facilitate the rapid vertical growth of plant. Screwpine uses involve the flavoring of jams and chutneys. They can also be used to make a paste that can be used in cakes and desserts. Wrapping of savoury dishes, such as chicken and sticky rice, is also done through screwpines.
4. Climbing Fig (Ficus pumila)
Ficus pumila, commonly known as climbing fig, is a flowering species belonging to the Moraceae family. It is a vigorous, fast-growing evergreen vine that can grow up to 15 feet or more when grown outdoors. It develops climbing roots and the roots arise from the internodes. Climbing roots are the roots which help in climbing.
5. Arjuna Tree (Terminalia arjuna)
Terminalia arjuna, commonly known as the Arjuna tree, is a deciduous buttress tree which belongs to the Combretaceae family. It usually has a large buttressed trunk with a spreading crown and drooping branches. The striking buttress roots of this tree provide stability to the plant in poor soil conditions along with riverbanks where these trees are often found. The Arjuna tree is usually found in the Indian sub-continent near the river banks, and can also be found in other countries such as Malaysia, Kenya, and, Indonesia. Based on observations of various physicians, it is found that the bark of this tree can be used for various medicinal purposes like anginal pain, hypertension, congestive heart failure, and dyslipidemia.
6. Cotton Tree (Bombax ceiba)
Bombax ceiba, commonly known as the cotton tree, is a large deciduous tree that belongs to the Malvaceae family. These trees are large, fast-growing tropical trees which can grow up to a height ranging between 20-25 metres and can spread 8-15 metre wide, but in wet tropical regions they can reach up to a height of 60 metres. Cotton trees have erect stems which develop buttress roots to provide support to the plant. The Semal tree (Bombax ceiba) is considered one of the most massive Bombax ceiba all over the world and is located in the Shivalik Bhabar range. Medicinal uses of this plant include-
- Decoction of the bark is given orally to combat fever
- Diabetics should take a decoction of the heartwood
- Bark juice is given to reduce stomachache
- A product is prepared from Bombax along with other plants to treat pimples and skin eruptions
Moonseed, scientifically known as Menispermum canadense, is a dioecious, scrambling, twining (no tendrils), woody vine which will typically grow to 8-20 feet long when twining its way through the vegetation. If there are no support structures available, it will spread indefinitely along the ground, forming a dense ground cover up to 12 inches high. Common moonseed contains assimilatory roots, which are modified adventitious roots that turn green and carry out photosynthesis. These plants are highly toxic in nature.
8. Ludwigia Sedioides
Ludwigia Sedioides, commonly known as the Mosaic plant, is a beautiful floating aquatic plant which belongs to the Onagraceae family. It is usually found in freshwater ponds, but can also thrive in an aquarium tank under favorable conditions. Ludwigia sedioides contain floating roots. These roots are spongy and filled with air, which helps the plant to stay buoyant for floating. The roots make the plant inflated so that the plant can float over the water surface. These free-floating plants (having no roots anchored in soil) can draw the maximum amount of nutrients directly from the water.