Adventitious root modification

Adventitious root system

Root developing from any part of the plant other than radicle is called adventitious root.  

It may develop from the base of the stem or nodes or internodes. Example: Monstera deliciosa, Ficus benghalensis, Piper nigrum. In most of the monocots the primary root of the seedling is short lived and lateral roots arise from various regions of the plant body. These are bunch of thread-like roots equal in size which are collectively called fibrous root system generally found in grasses. Example: Oryza sativa, Eleusine coracana, Pennisetum americanum.

Adventitious root modification

a. Storage roots

1.  Tuberous root

These roots are swollen without any definite shape. Tuberous roots are produced singly and not in clusters. Example: Ipomoea batatas.

2.  Fasciculated root

These roots are in cluster from the base of the stem Example: Dahlia, Asparagus, Ruellia.

3.  Nodulose root

In this type of roots swelling occurs only near the tips. Example: Maranta (arrow root) Curcuma amada (mango ginger), Curcuma longa (turmeric)

4.  Moniliform or Beaded root

These roots swell at frequent intervals giving them a beaded appearance. Example: Vitis, Portulaca, Momordica, Basella (Indian spinach).

5.  Annulated root

These roots have a series of ring- like swelling on their surface at regular intervals. Example: Psychotria (Ipecac)

b.  Mechanical support

1.  Prop (Pillar) root

These roots grow vertically downward from the lateral branches into the soil.

Example: Ficus benghalensis (banyan tree), Indian rubber.

2.  Stilt (Brace) root

These are thick roots growing obliquely from the basal nodes of the main stem. These provide mechanical support.

Example: Saccharum officinarum, Zeamays, Pandanus, Rhizophora.

3.  Climbing (clasping or clinging) roots

These roots are produced from the nodes of the stem which attach themselves to the support and help in climbing. To ensure a foothold on the support they secrete a sticky juice which dries up in air, attaching the roots to the support. Example: Epipremnum pinnatum, Piper betel, Ficus pumila.

4.  Buttress root

In certain trees broad plank like outgrowths develop towards the base all around the trunk. They grow obliquely downwards and give support to huge trunks of trees. This is an adaptation for tall rain forest trees. Example: Bombax ceiba (Red silk cotton tree), Ceiba pentandra (white silk cotton tree), Terminalia arjuna, Delonix regia, Pterygota alata.

c.  Vital functions

1.  Epiphytic or velamen root

Some epiphytic orchids develop a special kind of aerial roots which hang freely in the air. These roots develop a spongy tissue called velamen which helps in absorption of moisture from the surrounding air. Example: Vanda, Dendrobium, Aerides.

2.  Foliar root

Roots are produced from the veins or lamina of the leaf for the formation of new plant. Example: Bryophyllum, Begonia, Zamioculcas.

3.  Sucking or Haustorial roots

These roots are found in parasitic plants. Parasites develop adventitious roots from stem which penetrate into the tissue of the host plant and suck nutrients.

Example: Cuscuta (dodder), Cassytha, Orobanche (broomrape), Viscum (mistletoe), Dendrophthoe.

4.  Photosynthetic or assimilatory roots

Roots of some climbing or epiphytic plants develop chlorophyll and turn green which help in photosynthesis. Example: Tinospora, Trapa natans (water chestnut), Taeniophyllum.