In some plants, roots change their shape and structure to become modified. These modified roots perform functions other than absorption and conduction of water and minerals.

Tap root modification for storage of food:

A) Fusiform roots/Spindle roots - These roots are thicker in the middle and tapering on both ends, eg. Radish (Raphanus sativus)

B) Conical roots - These roots are thicker at their upper side and tapering at the lower side, eg. Carrot (Daucus)

C) Napiform roots - These roots become swollen and spherical at the upper end and tapering (like a thread) at their lower end. Eg. Turnip (Brassica rapa), Beetroot (Beta vulgaris)

D)Tuberous roots - These roots do not have a regular shape and any portion of roots become swollen & fleshy. Eg. Mirabilis.

E) Nodulated roots - Nodules are formed on branches of roots by nitrogen-fixing bacteria (Rhizobium). Eg. Plants of Papilionaceae subfamily of Leguminosae.

Modification of Root - Tap root modification for respiration

Modification of Root - Tap root modification for respiration

Pneumatophores:

Halophytes are the plants that grow in marshy or swampy areas.
There is a severe shortage of oxygen in swampy soils.
Therefore, the plants growing in these areas, for example, Rhizophora, the roots come out of the soil and grow vertically upwards.
These roots, that are negatively geotropic and positively phototropic are called pneumatophores.
The pneumatophores have numerous pores that allow the diffusion of oxygen.
These pores are called lenticels.
These roots are non-photosynthetic.

Modification of Root - Adventitious root modification for storage

Modification of Root - Adventitious root modification for storage

Like tap roots, the adventitious roots of some plants are modified for the storage of food.

Simple Tuberous Roots:

These are creeping and swollen adventitious roots.
These do not have a definite shape.
These arise from the nodes of the prostate stem and grow towards the soil.
These appear singly.
For example, Ipomoea (sweet potato)

Fasciculated Tuberous Roots:

These are the modified adventitious roots that appear in clusters.
They have a definite shape.
For example, Asparagus, Dahlia etc.

Nodulose Roots:

These are the modified adventitious roots in which the apices are swollen.
These are seen in ginger, turmeric, etc.

Beaded or Moniliform Roots:

These are modified adventitious roots that appear beaded due to alternate swollen and constricted region.
For example, Momordica

Annulated Roots:

These roots appear as if number of discs are placed one over the other.
This type of appearance occurs due to series of swollen regions.
For example, Cephaelis ipecacuanha

Modification of Root - Adventitious root modification for support

Modification of Root - Adventitious root modification for support

In some plants, adventitious roots are modified to provide support.

Prop Roots:

These are the hanging structures that can be prominently observed in a banyan tree.
These develop from branches and grow vertically downwards.
They ultimately penetrate the soil to provide support to heavy branches.
Hence, these behave like pillar to provide support to the parts of the tree.

Prop Roots in Banyan Tree

Stilt Roots:

The stem of maize and sugarcane bears roots coming out from the lower nodes.
These are called the stilt roots.
These roots mainly occur in monocots and shrubs.
They grow downwards and penetrate the soil.
They are mainly concerned with providing support to the stem just like ropes provide to tent.

Stilt roots

Climbing Roots:

These roots are seen in weak climbers.
These roots come out from the nodes of the stem and allow the plant to attach and climb over the support.
For example, money plant, black pepper, etc.

Clinging Roots:

These are seen in epiphytic plants.
They fix themselves in the crevices of tree trunk and allow the attachment of the epiphyte.
For example, orchids.

Buttress Roots:

These arise from the basal part of the stem and spread in all directions.
These are vertically elongated and horizontally compressed.
These appear like planks.
For example, Ficus.

Modification of Root - Adventitious root modification for additional functions

Modification of Root - Adventitious root modification for additional functions

Apart from acting as storage organs and providing support, adventitious roots also perform a number of additional functions in some functions.

Epiphytic Roots:

Epiphytes are the photosynthetic plants that grow on horizontal branches of trees to obtain sunlight.
They have special hanging roots called epiphytic roots.
These roots have a spongy tissue called velamen which helps in absorption of moisture from the atmosphere.
These roots are also called assimilatory roots because of their photosynthetic activity.

Sucking roots or haustoria or parasitic roots:

These are specialised microscopic roots present in parasitic plants to obtain nourishment from the host plant.
These can penetrate xylem and phloem elements.
For example, cuscuta, viscus, etc.