Asexual Reproduction in Plants

Types of asexual reproduction in plants

Plants naturally present two main types of asexual reproduction:

Fragmentation

In this type of asexual reproduction, a new plant forms from a part or fragment of the original plant. It is commonly called “vegetative reproduction or propagation” because the fragment originates from a vegetative organ of the plant (stems, roots, or leaves) and not from a reproductive organ (flowers in angiosperms).

Fragmentation is the most common type of asexual reproduction in plants and the fragments are usually modified stems, roots, or leaves. This type of asexual reproduction is based on the presence of meristems in these parts of the plant and the ability of parenchymatic tissue to differentiate into other types of tissue when needed. Moreover, plants are able to develop roots in other parts of the plant beside the main root, known as adventitious roots, which also aid in asexual reproduction.

Some of the most common vegetative parts that plants use for asexual reproduction are:

• Rhizome: ginger.

• Stolon: strawberry.
• Bulb: onion.
• Tuber: potato.
• Corm: taro.
• Plantlet: kalanchoe.

Apomixis

Some plants evolved a different type of asexual reproduction using sexual structures but without undergoing fertilization. In apomixis, a diploid cell in the ovule originates an embryo, and the ovule develops into a seed (and the ovary into a fruit). Thus, no haploid gametes are produced, and the embryo is a clone of the parent plant.

Diagram of asexual reproduction in plants

The below shows diagrams and images of different structures used by plants for vegetative asexual reproduction.

Figure 1: Types of structures for vegetative reproduction in plants. A) tuber, B) rhizome, C) stolon, D) corm, E) bulb, and F) plantlets. Source: A) MartinThoma, CC0, B-D) Pearson Scott Foresman, Public domain, E) RoRo, CC0, all via Wikimedia Commons, F) Udik_Art, free use, pixabay.com.

Examples of asexual reproduction in plants

Advantages and disadvantages of asexual reproduction in plants

Asexual reproduction can have many advantages for plants, or other organisms, under the right conditions (which we will discuss shortly). Some of these advantages for plants are the following:

• It does not require the investment of resources for producing flowers, seeds, and fruits, which are high resource-consuming processes.
• Faster development. The new plant reaches maturity faster and has higher survival probabilities. The new plant avoids the seed germination stage, where seeds and developing seedlings are very vulnerable to predation, pathogens, wildfires, and other external conditions.
• Traits highly adapted to an environment are passed on without modifications (excluding mutations) to the clones.
• Increased number of progeny. Creating clones is less resource-consuming, thus, a plant can generate more clones and more quickly, than sexually produced progeny. This allows for rapid increases in population size in a relatively short time.

The first two advantages do not really apply to reproduction through apomixis, as seeds are still produced. However, the parent plant can save some resources by not waiting for male gametes and have the advantage of seed and fruit dispersals which enable plants to reach more distant locations.

In summary, asexual reproduction is usually more advantageous than sexual reproduction in stable environments where individuals are not faced with new threats or environmental changes. Under stable conditions, a clone would encounter the same environment as the parent plant and the inherited traits would likely be highly adapted to that environment.

Artificial methods of asexual reproduction in plants

Methods used in agriculture and horticulture are considered artificial methods of plant reproduction because they involve some level of human manipulation. Some of these methods just take advantage of the natural vegetative propagation methods that plants use or accelerate them.

• Grafting: a stem section of a plant, the scion, is grafted onto the stem of another plant that is rooted, the stock. To do this, both stems are cut obliquely so the matching surfaces fit when they are tied up together. The result is that the vascular systems of the two plants fuse and can grow as one organism which is called a graft. With this method, desirable traits of both plants can be maintained (like the fruits of the scion and the root characteristics of the stock).
  • It is commonly used for some varieties of roses, citric fruits, and grapes.
• Cutting: a stem section that contains some nods is cut and placed in soil. The fragment will develop roots and shoots. Some plants’ stems will also develop when placed in water.
  • Examples of plants reproduced with cuttings are coleus and money plants.
• Layering: a part of a young stem or branch that can be easily bent while still attached to the plant. After some time, the buried part of the stem will develop roots and can be removed to be transplanted.
  • Plants that can be reproduced this way are jasmines and bougainvillaea (paper flowers).
• Suckering: in many shrubs and trees, sprouts appear from the root system (usually rhizomes), called suckers. These suckers can be cut out and planted to get new plants, but they are also commonly pruned in crops when they appear in excess as they consume resources from the parent plant.
• Tissue culture: plant tissues are commonly cultured under laboratory conditions for agricultural or conservationist research. Several types of plant tissues or cells can be used which are placed in a nutritious medium. A mass of cells forms first and eventually a large number of plantlets develop that can be transplanted.

Figure 2: Examples of artificial methods of asexual reproduction in plants. Left: layering, right: grafting where A is the scion and B is the stock. Source: both images Pearson Scott Foresman, Public domain, via Wikimedia Commons.