Plants grow, adapting to their surroundings. The plant structure has two main organ systems, the shoot, and the root system. The shoot is the upper part of the plant responsible for reproduction and food. The root is the underground part responsible for fixation and absorption.
The environmental conditions and plant needs change the functions of these organs. Shoots change for support and anchorage while being reproductive. They divide into the underground stem, subaerial stem, and aerial stem. The underground stems become food storage units growing below the ground level. Please read below to know more about underground stems and their examples.
Examples of shoots and roots modifications
The shoot system includes the stems, leaves, and flowers. The root system consists of the primary, secondary and tertiary roots. These organs change to adapt to environmental stress. To understand shoot and root examples of plant modifications, we must understand their role.
The roots, apart from fixing and absorbing, also perform other roles. Some plants provide food storage, plant growth, and extra support. The root modification examples are storage roots, pneumatophores, adventitious roots, prop roots, etc.
The shoot modifies its leaves, stems, and flowers to adjust to the surroundings. The stem is the upper part in charge of support and reproduction. It has nodes that propagate leaf growth. Due to environmental stress, the stems also provide other roles. It supports food production and storage, water storage, and absorption. Examples of stem modifications are thorns, underground stem- rhizomes and tubers, etc.
The leaves also change to environmental conditions and provide water and food storage. It becomes the spine in some plants and protects them from predators. Examples of leaf modifications are bulbs, leaf tendrils, traps, spines, etc.
What is an underground stem?
Underground stems are stem tissues modified to grow under the soil. They are the storage unit of food and nutrients. They are the organs of vegetative growth and perennation (the ability to survive seasons).
The primary role of any stem is to transport water and nutrients from roots to leaves. It also conducts food and nutrients from leaves to the rest of the plant body. But an underground stem is below ground and functions as a stem and behaves like other organs. Depending on its environmental stress factors, it fulfils the role of a root, leaf, stem, node, etc.
The underground stem reproduces through the asexual method. They have nodes as signs of new cell growth. During the nonvegetative period, like extreme climatic seasons, the plant stays dormant. Since it’s below the ground, it’s not affected by abrupt climate change or predators. Herbivores consume the upper part of the plant, leaving the underground stem safe, thus protecting the vegetative layer from overgrazing.
What are the types of underground stems?
There are five different underground stems, depending on the structure and functions. Their functions depend on the plant’s needs and its environmental stress. Here are the five types listed below with examples.
- Bulb– It is a short and upright structure. The stem changes into a thick starch storage unit underground. e.g., Onions
- Corm– It is short upright and has a thick starchy stem. Outer layers are thin and papery. e.g., Taro or Colocasia
- Rhizome– It has scale-like leaves and nodes. The nodes shoot upwards and root downwards. e.g., Ginger
- Stolon– This is a horizontal underground stem with nodes and long internodes. Found on the topsoil. e.g., Strawberry, Mint.
- Tuber– The stem is large, fleshy, and full of starch. They have nodes for propagations. e.g., Potato, Onions.
Functions of ginger as a rhizome
The rhizome is a type of underground stem that is thick and has reduced scale-like leaves. It has a node and short internodes that helps in vegetative growth.
Ginger is a rhizome as it has nodes and short internodes. These nodes allow shoots to grow upward and roots below. Unlike stolons or runners, these are individual plants that grow in a continuous pattern. The rhizome of the ginger plant stores starch, nutrients, and food content. The stored food helps when the plant has to propagate further. The dormant phase is also possible because of these storage units.
Underground stem ginger is a rhizome because of the presence of the following,
- Nodes and internodes – these help in vegetation propagation
- Scaly leaves – modification from stem system
- Starch storage in stem etc.
It also produces leaves upwards and roots below the soil, making it an ideal middle organ, a stem.
Conclusion
Modifications occur in the plants due to environmental factors. These are gradual modifications and do not happen overnight. Plants change due to environmental stress like oxygen level, sunlight, and nutrients. These changes help them survive and grow further. One such adaptation in plants is the underground stems. These stems grow below the ground and support propagation. It is also rich in starch and has dense nutrient value as they have storage tissues. Farmers depend on these plants for steady growth as they withstand extreme climates. Some underground stem examples are onions, gingers, potatoes, etc. The steady growth of these also helps in maintaining soil fertility.