Adventitious roots are those that grow from places excluding the radicle of the plants. An adventitious root structure is made up of a collection of its kind of roots and their branching. The root system of an adventitious plant might be subterranean or aerial. They originate from stem nodes, intermodal, leaflets, and other sources. Monocotyledonous plants produce them as well, and they are made up of root primordial cells. This blog will cover all aspects of the adventitious root system, including types and modifications, as well as its examples. So without any further ado, let’s get started.
Modifications of Adventitious Root System
Adventitious roots undergo many modifications to facilitate the plant in many ways. These roots are been modified to support the parts of a plant in the following described ways:
- To store the food
- To provide mechanical support to the plant
- To carry out other essential functions of the plant
Here is a detailed flowchart showing the modifications of the adventitious root system.
Root Type Modification Chart
We will go through each modification to know more about its details.
Modified Roots For Storage of Food
Tuberous roots are a type of adventitious root that has been modified to facilitate storing of food. They are squishy, have no distinct form, and frequently swell. Shoots emerge through one end of these tuberous roots, whereas roots emerge from the other. Examples of tuberous roots include Sweet Potato or Ipomoea batatas.
The enlarged roots, often known as root tubers or fasciculated roots grow in groups. They are found directly beneath the base of the Dahlia stem. The fasciculated mushy roots of Asparagus appear at distances on the regular roots. Dahlia, Ruellia, and Asparagus are examples of fasciculated roots.
The moniliform roots are another variation of the adventitious roots. These roots are enlarged as well. The enlargement of moniliform roots, on the other hand, happens at periodic intervals, giving the roots a necklace-like beaded look. Examples of Moniliform Root Type are Rose moss, Momordica, Indian Spinach, Basella, and some grasses.
The alteration of adventitious roots that are inflated at the apex or ends is known as nodulose roots. They have a distinct appearance. Turmeric is a good example of nodulose roots. These roots possess a characteristic shape that differs from other root systems.
A succession of manifestations in the form of rings is seen on the surface of modified adventitious roots of this kind. These outward manifestations appear to be disc-like structures stacked one on top of the other. Ipecac, or Cephaelis ipecacuanha, is a great example of annulated roots.
Modified Roots For Mechanical Strength
Some roots are modified to facilitate the plant in giving it strength and support. This mechanical support helps the plant to grow by giving it tensile strength. These roots have been classified into four major types: Prop or Pillar roots, Stilt roots, Climbing roots, and Buttress roots. We will see all these types of roots to know more about their characteristics.
Prop or Pillar Roots
- The word “Pillar” means that these roots help in strengthening the plant. These are the types of adventitious roots that develop from the downward branches of the tree.
- Modification of these roots occurs in order to sustain the large and heavy branches of the tree.
- Prop roots are hygroscopic in nature. That means, they collect water from the air and turns red in color due to moisture absorption.
- The tips of prop roots possess root caps. Prop roots grow robust and pillar-like when they reach the surface. During this phase, it becomes tough to observe the difference between the trunks and the prop roots.
- Example: Banyan Tree, Mangrove Plant
Stilt roots are small, thick sustaining roots that grow diagonally from the stem’s basal nodes. These roots develop in swirls in Sugarcane, Maize, Pennisetum, and Sorghum. They establish fibrous roots following reaching the soil to give support for the long and thin jointed and unbranched stems, similar to pillar or tent ropes. They also facilitate the intake of water and mineral ions. Stilt roots grow solely from the bottom surface of the inclined stem in Screwpine or Pandanus Odoratissimus to give support. They are also known as prop roots since they are single-sided. Pandanus has many folded different caps on its supporting roots.
Climbing roots are found in the climbers: the plants that need proper support to grow and adhere to the surface. These roots are non-absorptive and tend to penetrate the fissures of other structures in order to facilitate growth. These roots secrets juicy, sticky material from its tip that helps in supporting the plant firmly. A well-known example of tendrillar climbing root is the Vanilla Planifonia plant. Another type of climbing root is also known as clinging roots. These types of roots may emerge from each node and then they get branched. Examples of climbing or clinging roots are Tecoma, Hedera, and Climbing Fig.
Buttress roots form at the stem base and aid in the preservation of the plant’s internal structure. The vertically prolonged base section of the stem expands in diverse directions in the soil. The appearance of these altered adventitious roots is that of planks. Some great examples of these buttress roots include the Cotton tree, Arjuna tree, and Moreton Bay Fig tree.
There are some roots that perform special functions in order to support the plant in its growth. Such roots are categorized as Assimilatory roots, Epiphytic roots, Floating roots, Mycorrhizal roots, Sucking roots, and Reproductive roots. Let us learn about each type of root and the functions they perform in detail.
All the vital functions of the plant are carried out by these types of roots. Assimilatory roots are responsible for carrying out important functions such as photosynthesis. With the help of green roots and chlorophyll, they can perform photosynthesis and carry out major activities in the plant. These kinds of roots are highly branched for increasing their surface area. With the expansion of the surface area, the maximum sunlight can be absorbed by the plant. Examples of assimilatory roots may include Water Chestnut, Ribbon roots, and Moonseed.
Epiphytic or Aerial Roots
Epiphytes are plants that depend on other different plants for their nutrition and shelter. Epiphytic roots generally lie on the surface of epiphytes. These roots can be irregularly shaped and they tend to hang down on the surface of other plants for their growth. In this type of root, the root cap is not present. However, they possess a dead spongy tissue, called velamen. Such roots are hygroscopic, which means they utilize velamen for absorbing excess water from the soil. Orchid, Vanda, Denbrodium, etc. are some of the examples of Epiphytic or Aerial roots.
Adventitious roots such as floating roots are found in many aquatic plants. It arises from the node of the horizontal stem plants. Some of these roots stores water and swell up or become inflamed. These inflated roots help the plant float in water. Also, these roots can also involved in the exchange of certain gases. Hence, they can also be referred to as respiratory roots. An example of this well-known root system is Ludwigia.
Another type of adventitious root system which you might not have heard of is mycorrhizal roots. Mycorrhizae mean the symbiotic relationship between fungus and a higher plant. This symbiotic relationship is built when the fungus absorbs the nutrients within the soil. Then, the plant supports this fungus with organic food. Some of its renowned examples are Pine, Snow Plant, and Monotropa.
Haustoria or Sucking Roots
Parasites absorb nutrients from the host. To facilitate this function, they produce microscopic roots, known as sucking roots or Haustoria. The significance of the term “Haustoria” is these roots are also found in non-green parasitic shrubs and plants. To collect nutrition, sucking roots emerge from the node and delve deeper into the connecting tissue of the recipient. Cuscuta and Mistletoe are the most common examples of Sucking roots. Reproductive roots are the kind of adventitious roots that help plants in their reproduction. These roots first develop the buds that later turn into the shoot to facilitate the process of reproduction. These roots, if cut and planted into the soil, can give rise to the new growth of a plant. These roots can also be the way of processing vegetative propagation in plants. Examples of Reproductive roots include Dahlia and Sweet Potato.