If you’ve ever propagated one of your houseplants, you likely have a good idea of what the process of vegetative propagation looks like. One plant superpower that many invasives have is the ability to grow a new individual from a fragment of root or stem; however, not all plants have this ability. This blog is part of a series of posts called How Do Plants Work?
All plants are made of the same basic building blocks, but vegetative propagation is another example of different plants evolving to use what they already have to their advantage. It also serves as a great example of just how complicated some processes in plant biology can be!
Propagation is a term used to describe the growth of a new individual from a parent plant. Propagation can be sexual or asexual – plants grown from seeds with two parent plants were propagated sexually, while plants grown from seeds with one parent plant were propagated asexually. Another form of asexual propagation is vegetative propagation. Both forms create plants that are essentially clones of the parent plant.
Types of Plant Cells
To understand all of the pieces that come into play in order to make vegetative propagation possible, we’ll go over the different types of tissue found in all plants.
- Dermal tissue: covers the surface of the plant, protecting it from the outside world.
- Ground tissue: makes up the ‘body’ of plants.
- Vascular tissue: acts as the transportation network throughout the plant for water, nutrients, signals, etc.
These three types of tissue are found in all plants and in all parts of the plant. However, each type of tissue can be divided into subtypes. Subtypes result from plants adapting to create specialized versions of the ‘basic’ tissue.
Stem Construction
Stem construction follows some basic patterns. Along the stem, nodes are spaced out and separated by empty stretches of stem called internodes. The nodes are where the leaves attach to the stem, and typically an axillary bud will be in the crease between the leaf and stem.
Axillary buds contain highly-regulated gradients of different plant growth hormones within them. If any of the carefully-arranged growth hormones are disturbed, the axillary meristem will initiate the growth of a new stem. This same concept applies to roots. Found throughout root systems are root meristems, responsible for stimulating new root growth.
Plant Growth Hormones
Like animals, changes in plant growth are directed by changes in hormone concentrations within the plant. A very large number of plant hormones control a vast array of processes of plant growth, but one of the most important is auxin. The regular flow of auxin throughout the plant is important for regulating and promoting the growth of the plant and keeping it healthy.
Cutting the tip of a plant off disrupts the flow of auxin around the plant. The auxin starts accumulating in the new cut area, and this increased concentration of growth hormone causes nearby axillary meristems to begin growing. In some plants, the axillary meristems are far apart and few, but others are close together and numerous. This is why trimming stimulates growth in some invasives!
While all plants will have a change in the flow of auxin after being trimmed, not all plants can grow roots from fragments of stem, or shoots from a fragment of root. Plants that can generate entirely new plants from cuttings have a gene that other plants don’t have. It activates within the ground tissue of the fragments as a response to the stress of being cut, and activates the growth mechanisms present in the fragment.
Vegetative reproduction in invasive plants
English Ivy can form roots to grasp onto vertical surfaces anywhere along the plant. Cuttings of this plant can also sprout new roots and grow into a new individual if left on the soil.
Himalayan Blackberry can form roots at the tips of its long canes and become rooted before forming a new plant. New plants can also grow from nodes along the canes and from cuttings if left on the soil.
Yellow Lamium can grow new plants from fragments of its roots or stems. Roots can also form along the stem, spreading the plant further.
References
- Taiz, L., Zeiger, E., Møller, I. M., & Murphy, A. S. (2015). Plant Physiology and Development (6th ed.). Sinauer Associates Inc.
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