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Plant Stem

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Plant Stem

What would you think if I told you that one of the most versatile plant parts is the stem? I’m not kidding, you can fry them, mash them, or even base your state’s entire personality off of them. And no, I am not talking about celery stalks, but potatoes. That’s right, the beloved potato is actually a plant’s stem! The plant stem is a plant organ that helps support other plant parts, transport nutrients, store food, and sometimes even reproduce!

What is a plant stem?

The plant stem is an organ part of the plant shoot system along with the leaves. The stems support many other plant parts including the leaves, flowers, fruits, buds, and branches.

Besides support, stems also provide transport of water and nutrients throughout the plant. The stem of a plant is typically above ground and functions as the main body of the plant. Stems come in a variety of different forms, they may be branched or unbranched and may be underground as well (tubers, rhizomes, etc.)

Plant stem definition

So how exactly would you define a plant stem? They come in many different shapes and sizes, and sometimes are specialized to perform specific functions. Overall, we can say that the plant stem is a supportive plant organ, typically growing aboveground, and supporting the buds, leaves, and sexual reproductive structures.

Plant stems are organs that are part of the main plant body supporting other shoot system organs and growths (leaves, sexual structures, buds), and are involved in transport and storage as well.

The functions of the stem in plants

The stem has a number of functions that earn it its role as the plant organ that functions as a central body. The functions of plant stems include:

  1. Transport of water through the xylem tissue from roots to leaves. Additionally, transport through the phloem of products from photosynthesis to other parts of the plant.

  2. Support the leaves so that they may access sunlight and water for photosynthesis.

  3. Storage of both water and nutrients.

  4. Perform photosynthesis in some cases, as green (often called herbaceous) stems can photosynthesize.

Stems versus their environment

Plants have adapted to many habitats, from the tundra to the desert. This means that plant stems vary greatly. One example of a plant stem specially adapted to its environment is that of the cactus. Cacti thrive in dry environments (such as deserts) and therefore have extremely reduced leaves or even none at all! The stems of cacti can photosynthesize to make up for the lack of leaves. They are also fleshy or succulent to help store water for when it is sparse!

Structure of the plant stem: diagram

Nodes are points on the stem where the leaves may grow from. Between them, are the internodes, which are the spaces on the stem between nodes.

The axillary buds may develop in the area where the petiole of the leaf connects to the stem, known as the “axil”. The term bud refers to an undeveloped shoot that may become a flower, leaf, or perhaps a branch, which is an extension of the shoot system and will have its own node-internode pattern (Fig. 1).

Figure 1: Diagram of the basic stem structure of a plant. Source: StudySmarter Originals.

Cells and tissues of the plant stem

The stem and the parts it supports (shoot system) develop from the region of the embryo known as the shoot apical meristem. This region is made up of meristematic tissue, which is the undifferentiated tissue associated with cell growth and division. As the plant grows, the shoot apical meristem maintains apical dominance, meaning it inhibits the development of lateral buds as necessary so that the plant can grow vertically towards the direction of light.

Like other parts of the plant, the stem also contains the three types of permanent tissue: dermal, ground, and vascular. These tissues have specific functions in the stem and their cells are specialized to perform certain functions, which means they are differentiated.

Dermal tissue covers stems, just as it does the other plant organs, roots and leaves. The epidermal cells of stems may be specialized to be stomata or trichomes, like on leaves.

Stem adaptations for plant defense

Thorns, prickles, and trichomes are all physical structures that make accessing the stem of plants less accessible to hungry herbivores and omnivores because they poke and sting. But some plants go so far as to recruit their own personal security guards. The acacia tree has specialized thorns, that grow large and provide fully stocked condos for the ants, and in return, the ants protect the tree from hungry animals by attacking and stinging them!1

Vascular tissue is an essential part of the stem as the main plant body, and thus, the main route of transport between the roots and leaves. Ground tissue also plays a big role in stems as a storage tissue.

Primary versus secondary growth in stems

Primary plant growth contributes to the initial growth of the stem and its lengthening (Fig 2). The apical meristem controls this stem elongation, encouraging the plant to grow taller. Some plants only ever experience primary plant growth- i.e. most herbaceous plants.

Secondary growth contributes to the thickening of the stem. Secondary growth is controlled by the lateral meristem. The lateral meristem consists of the vascular cambium and the cork cambium. These cambium tissues are meristematic and can produce new tissue through cell division.

The vascular cambium cells divide to produce secondary xylem inside and secondary phloem outside. As the newer tissues are produced the older xylem tissues are pushed to the center of the stem in plants experiencing secondary growth where they provide support for the plants.

Secondary plant growth helps provide extra support for plants that grow larger (Fig 2). Having the cork cells and the old xylem (fortified with lignin) provides extra layers of support as plants continue vertical growth. That is why the tree growth form is characterized by an increase in width or secondary plant growth. Some herbaceous plants may experience the production of the secondary xylem and phloem but not the production of cork cells- as that would make them woody. Plants that have bark formed from the cells of the cork cambium are considered woody.

Most secondary growth occurs in dicots and gymnosperms. Monocots do not often experience secondary growth.

Figure 2: Diagram of primary growth and secondary growth in stems. Source: StudySmarter Originals.

Types of plant stems

Plant stems, like roots and leaves, come in many different shapes and sizes and serve a number of specialized functions for certain plants. In fact, a lot of plant parts you eat are stems. Especially parts that people mistake for roots a lot of the time such as potatoes, garlic, and even ginger!

Vines

Vines are considered a plant growth form in which the stems of these plants rely on the support of other plants or objects for support. You may be familiar with some types of plants that exhibit this growth form including grapes or poison ivy. Vines tend to send out tendrils that allow them to grow and climb other plants. Some vines are considered parasitic and grow at the expense of other plants!

Rhizomes and stolons

Rhizomes are stems that grow horizontally under the soil. They may be adapted to provide extra food storage for the plant as well (such as in ginger plants) (Fig. 3). Stolons are also horizontally growing stems also known as runners. They usually grow just above or below the soil surface.

Both rhizomes and stolons have the ability to carry out vegetative reproduction. Vegetative reproduction is a method of reproduction where a plant produces new plant organs (roots and shoots) off of non-reproductive structures, and the new plant organs have the ability to exist as a separate plant. If a plant is in an environment with fewer resources, this method of reproduction may be more successful than investing a lot of energy into sexual reproduction.

Vegetative reproduction is the asexual reproduction of plants by producing vegetative plant parts (stems, leaves, roots) that can grow into new, independent plants.

Tubers, corms, and bulbs

Tubers are also modified stems that grow underground. Tubers are adapted to act as storage for a plant, often storing sugars in the form of starches. They are mainly composed of parenchyma tissue, which if you recall from learning about plant tissues, oftentimes functions as a storage tissue. This extra food storage and underground stem help some species survive winter conditions in seasonal climates (known as “overwintering”). Potatoes are one example of tubers, and the eyes of potatoes are actually buds that can form new plants via vegetative reproduction!

Bulbs and corms are similar to tubers in that they are short vertical underground stems that also store starches and food for the plant. Bulbs often have fleshy leaves (i.e. tulips) that are overlapping and may emerge when conditions are favorable or act as storage if not. Tulips, lilies, onion, and garlic are all common examples of plants with bulbous stems.

Corms often have scaly leaves, that are not overlapping like those of bulbs. Examples of plants with corm stems include crocuses and taro root (which is actually an underground corm).

Plant Stems Photos of plant stems (ginger, onion, taro root, and potatoes) Source: pixabay.com, edited. Figure 3: Examples of rhizomes (ginger- top left), bulbs (onion-top right), taro root (corms- bottom left), and potatoes (tubers-bottom right). Source: pixabay.com, edited.

Plant Stem - Key takeaways

  • Plant stems are organs that typically grow aboveground and are the main plant body.
  • The plant stem functions to transport water and nutrients, as storage organs, and to support the vegetative and reproductive plant parts.
  • Primary growth is observed when a stem is lengthening. Secondary growth contributes to the increase in girth in some plants which are typically called woody plants.
  • Some plant stems grow underneath the soil and function as starch storage (i.e., tubers) or may also help the plant carry out vegetative reproduction (i.e., rhizomes and stolons).
  • Tubers are also modified stems that grow underground. Tubers are adapted to act as storage for a plant, often storing sugars in the form of starches.

References

  1. Katherine Unger Baillie, "The mutualistic relationship between ants and acacias", Omnia Upenn, Oct. 31, 2019.

Frequently Asked Questions about Plant Stem

The stem is a plant organ that provides support to the leaves, buds, branches, and reproductive structures. 

The plant stem, being the main plant body, also transports water through the plant from the roots via the xylem tissue of the vascular system. The phloem tissue helps transport food the plant has produced to other parts of the plant body.


The stems of some plants are also adapted to store extra food for the plant. Green stems may also photosynthesize, although the main


Some stems have special structures that protect plants from herbivory (trichomes, thorns, prickles).

Plant stems occur in many different growth forms. 

If a plant has secondary growth and produces layers of cells from the cork cambium (meristem tissue) the plant is considered woody. Plants experiencing little or no secondary growth are known as herbaceous. Often the stem is the part of the plant appearing woody (as in tree trunks) or herbaceous (as in flower stalks). 


Vines are a plant growth form, in the stems which rely on support from other plants or objects. Vines send out tendrils to help them climb or grip surfaces. 


Other types of stems include underground, storage stems such as tubers, corms, bulbs, and rhizomes.


Rhizomes and stolons are horizontally growing stems that often are involved in the vegetative reproduction of new plants from vegetative (non-reproductive) plant parts. 

Plant stems are versatile organs with many functions. Therefore, examples of the stem range, from the underground tuber stems of potato plants to the thick trunks of maple trees. Taro, typically called taro "root", is actually a type of stem known as a corm, another type of underground storage stem. Having an underground storage stem helps plants overwinter in areas of colder climes.


Stems are often adapted to the particular climates that plants occupy. For example, cactus stems are often fleshy or succulent, meaning they are a good reserve for water storage, in arid desert environments. 


Typically identifying a stem means identifying the central axis from which leaves, buds, or branches are growing. Reproductive structures are also supported by the stem or its branches.

Plant "stem" cells are also known as meristematic cells or makeup meristem tissue. 

The meristem cells are undifferentiated cells that can differentiate to become any other kind of cell with a specific function. 


The plant meristem is found at the tips of the shoots (root tip as well) and in the developing buds. In particular, the shoot apical meristem helps elongate the main plant stem so that a plant can grow upwards towards the light. 


Plants may experience secondary growth, or an increase of girth in their stems, which is promoted by having lateral meristem tissues in the stem.

The stem of the flower supports the reproductive structures and helps bring nutrients and water to them through the vascular system. 

Stems can take many different shapes and forms. Stems may range from green thin aboveground stalks of herbaceous plants to the thick trunks of trees that have undergone secondary growth. 


Stems may also grow underground and take the form of tubers, corms, or bulbs. Stems may also be horizontally underground as in rhizomes. Runners are stems that grow horizontally connecting one plant to another plant and sometimes giving rise to new plants vegetatively (nonsexual reproduction). 


Examples of plant stems that may be consumed include garlic, potatoes, or ginger. 

Final Plant Stem Quiz

Question

Which of the following statements are true about plant stems?

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Answer

They are organs.

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Question

The stem supports many other plant parts including....

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Answer

leaves, branches, flowers, fruits, and buds. 

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Question

Which of the following is NOT a function of the plant stem?

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Answer

Absorbs water and nutrients from the soil

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Question

T or F: Stems do NOT grow belowground.

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Answer

False

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Question

Plant stems contain ____ and ____ tissue which is used for transporting water and nutrients throughout the plant body. 

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Answer

Xylem and phloem tissue

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Question

T or F: The stems of cacti can photosynthesize and store water.

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Answer

True 

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Question

______ are points on the stem where the leaves may grow from. Between them, are the _______.

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Answer

Nodes; internodes

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Question

The term bud refers to an undeveloped shoot that may become a.....


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Answer

Flower

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Question

The ______ _______ controls stem elongation, encouraging plants to grow taller to access light (sun). 

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Answer

Apical meristem

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Question

Which is not a type of plant stem that typically grows underground? 

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Answer

Vines

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Question

T or F: The primary growth of plants contributes to the lengthening of stems.

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Answer

True

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Question

Secondary growth increases the _____ of stems.

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Answer

Girth; thickness

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Question

What is the asexual reproduction of plants by producing vegetative plant parts (stems, leaves, roots) that can grow into new, independent plants called?

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Answer

Vegetative reproduction

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Question

The shoot system (stem and the parts it supports) develops from a region of the embryo known as the _____ _______ _______.

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Answer

Shoot apical meristem

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Question

Meristematic tissue is associated with the ______ and _____ _____ in plants. 

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Answer

Growth and cell division

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