Adventitious Root System: Overview & Modification in Roots

Flowering plants or angiosperms are specified by the presence of roots, stems, leaves, flowers, and fruits. These parts of the plants tend to show variations or adaptations as per the habitat they live in for protection, climbing, storage, etc. The part of the plant that grows below the soil (underground) is called the root system while the part of the plant which grows above the soil is known as the shoot system. The root system is the descending portion of the embryonal axis. It is positively geotropic, positively hydrotropic and negatively phototropic. There are three types of root systems; tap root system, fibrous root system, and adventitious root system. In this article, we will discuss the adventitious root system. 

Also Read: Parts of a Seed

Adventitious Root System

The root system which arises from any other part of the plants except the radicle such as stem nodes, internodes, leaf, etc. is known as the adventitious root system. The fibrous root system is also a type of adventitious root system. They can be underground or aerial. These types of roots are commonly seen in grasses, banyan trees, Monstera, etc.

Adventitious Root System

Modifications of adventitious roots

Adventitious roots are modified for different purposes like storage of food, providing mechanical support, reproduction, etc.

For Mechanical Support: 

There are three types of root modification for providing mechanical support to the plants. They are-

Prop roots/ Pillar roots: 

These roots are aerial roots that arise from the branches of the stem and later grow vertically downwards into the soil. They are very thick like a pillar and provide support to the main axis of the plant. They are mostly found in dicots. Example: Banyan tree-Ficus benghalensis.

Prop roots/ Pillar roots

Stilt root/ brace roots: 

They arise from the lower nodes of the stem and grow obliquely downwards into the soil. They are mostly seen in monocots. They support the two main axes of the plant. Example: Maize-Zea mays, Sugarcane-Saccharum officinarum, Screw pine-Pandanus

Stilt root/ brace roots

Climbing/clinging roots: 

These roots are found in climbers. They arise from nodes or internodes and help in climbing by penetrating the cracks or fissures. 

Example: Betel leaf-Piper betel, Black pepper- Piper nigrum, long pepper-Piper longum, money plant-Pothos

Climbing/clinging roots

For Food Storage: 

Adventitious roots also become swollen for the storage of food. Based on their shapes, tap roots are classified as: 

Tuberous roots: 

They are swollen roots, irregular in shape, and occur singly. Example-sweet potato-Ipomoea batatas

Tuberous roots

Fasciculated roots: 

They are a group/clusters of swollen and irregular-shaped roots. Example-Dahlia, Asparagus.

Fasciculated roots

Nodulated roots: 

These roots are swollen at the apex (tip). Example-Turmeric-Curcuma Domestica, Mango ginger- Curcuma Amada, etc.

Nodulated roots

Moniliform/ beaded roots: 

In this type, roots are swollen at regular intervals. They appear like beads in necklaces. Example-Bitter Gourd-Momordica, Portulaca

Moniliform/ beaded roots

Palmate roots: 

These roots swell like fingers in Palm. Example-Orchis (Orchid)

Palmate roots

Annulated roots: 

These roots appear in the form of ring-like swellings. The root swelling occurs in a series of rings that look like discs stacked one above the other. Example: Ipecac

Annulated roots

For vital functions:

Sucking/ Haustorial roots:

These types of roots occur in parasitic plants (non-green). These roots penetrate the xylem and phloem of host plants and draw nourishment from them. Example: Amarbail-Cuscuta reflexa (stem parasite), Cassytha filiform, Orabanda indica (root parasite).

Sucking/ Haustorial roots

Assimilatory roots: 

These are green roots that perform photosynthesis. Example-Aerial roots of Tinospora and submerged roots of water Trapa.

Assimilatory roots

Floating/ Respiratory roots: 

These types of roots are seen in the Jussiaea-an aquatic plant. They arise from the nodes or branches of the stem above the water level.

Floating/ Respiratory roots

Epiphytic/hygroscopic roots: 

These roots are found in plants that grow on other plants for shelter (epiphytic plants). They usually grow in dense canopy forests. They develop aerial hanging hygroscopic roots which absorb water from the surrounding atmosphere through a tissue known as velamen. Example: Orchids, Vanda

Epiphytic/hygroscopic roots

For other functions:

Epiphyllous roots: 

These roots arise from the base of the leaf margin for vegetative propagation. Example- Bougainvillea, Begonia.

Epiphyllous roots

Reproductive roots: 

These are the fleshy roots that develop into adventitious buds. Under favorable conditions, these buds can grow into a new plant. Example: sweet potato, dahlia

Reproductive roots

Root thorns: 

Roots are thorn-like hard and pointed arising from the stem above the ground. They protect the plants against herbivores. Example: Pothos, Armatus, Acanthorhiza

Root thorns

Things to Remember Based on Adventitious Roots 

• Root system is the part of the plant that grows below the soil.
• Shoot system is the part of the plant that grows above the soil. 
• There are three types of root systems; tap root system, fibrous root system, and adventitious root system.
• Adventitious Root system arises from any other part of the plants except the radicle such as stem nodes, internodes, leaf, etc. Example- grasses, banyan tree, Monstera.
• Adventitious roots are modified to provide mechanical support, to store food, for respiration, for photosynthesis and to perform other vital functions. 
• Prop roots, stilt roots and climbing roots provide mechanical support to the plants. 
• Tuberous roots, fasciculated roots, palmate roots, moniliform roots, nodulated roots and annulated roots are useful for storing the food. 
• Sucking/ haustorial roots penetrate the xylem and phloem of host plants and draw nourishment from them.
• Epiphyllous roots arise from the base of the leaf margin for vegetative propagation.
• Reproductive roots are the fleshy roots that develop into adventitious buds. Under favorable conditions, these buds can grow into new plants. 
• Some roots are thorn-lik and arise from the stem above the ground. They protect the plants from herbivores.