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Plant stem

life science Maturity 9-11 Next article →

A plant stem is one of two main structural axes in a vascular plant. The other main axis is the root.

Plant nodes c
Plant nodes c

Stems serve several vital roles for the plant's survival. They provide support to elevate leaves, flowers, and fruits toward the light. Stems also act as a transport system for fluids. They store nutrients and produce new living tissue through specialized cells. While most stems grow above the soil, some plants have stems that live underground.

Illustration of various types of plant stems
Illustration of various types of plant stems

To understand how a stem works, we must look at its internal anatomy. The stem is composed of three main tissue types: dermal, ground, and vascular tissue. Dermal tissue forms the outer protective layer. It often contains epidermal cells and can control gas exchange. Ground tissue surrounds the vascular tissue and helps with metabolic activities like respiration and photosynthesis. It also provides structural support.

Labeledstemforposter copy new
Labeledstemforposter copy new

Finally, vascular tissue handles long-distance transport. This tissue includes the xylem, the phloem, and the cambium.

The vascular system works like a network of pipes. The xylem tissue arises from the cells facing the inside of the stem. It moves water and minerals upward using transpiration pull, capillary action, and root pressure. The phloem tissue arises from cells facing the outside. It consists of sieve tubes and companion cells. The phloem distributes food, such as sugars, from photosynthetic tissues to the rest of the plant.

Translocation from the source to the sink within the phloem
Translocation from the source to the sink within the phloem

The cambium is a layer of tissue that sits between the xylem and phloem. The cambium divides to produce new xylem or phloem cells.

Stems are organized into specific repeating units. Nodes are the points where leaves or twigs attach to the stem. Nodes are small growth zones that can hold one or more leaves. Between two successive nodes is the internode.

Polygonum amphibium (4973671699)
Polygonum amphibium (4973671699)

Internodes can elongate to increase the distance between nodes. At the nodes, plants may also produce axillary buds. These buds can grow into new branches, flowers, or cones. Some plants even grow adventitious roots, such as brace roots, directly from these nodes.

Different types of plants have unique stem structures. In dicot stems, vascular bundles usually form a distinct ring around a central pith. Many woody dicots undergo secondary growth. This happens when the vascular cambium and cork cambium divide. The vascular cambium creates secondary xylem (wood) to the inside and secondary phloem to the outside. As the stem grows wider, a cork cambium develops to create a waterproof periderm. This replaces the original epidermis.

Royal Palm Trunk
Royal Palm Trunk

In contrast, monocot stems have vascular bundles scattered throughout the stem. Most monocots do not produce secondary growth and are not woody. Gymnosperms, like pine or spruce, are always woody. Their xylem contains tracheids rather than the vessels found in dicots.

Stems are highly specialized for different environments. Some stems are arborescent, meaning they form a single woody trunk like a tree.

Redwood M D Vaden
Redwood M D Vaden

Others are acaulescent, appearing stemless because the stem is extremely short. Some stems, called cladodes, are flattened and look like leaves to help with photosynthesis. Underground stems can also be very specialized. A tuber, like a potato, is a swollen stem used for storage and reproduction. A rhizome is a horizontal underground stem used for storage and reproduction. A bulb, such as an onion, is a short vertical underground stem with fleshy storage leaves.

Humans rely on stems for many essential resources. We eat many stem-based crops, including asparagus, bamboo shoots, and kohlrabi.

Asparagus produce-1
Asparagus produce-1

Sugarcane stems are a primary source of sugar, and maple sugar comes from tree trunks. We even harvest spices like cinnamon from the bark of tree trunks. Wood from many stems is used for building houses, making furniture, and producing paper. Even medicines, such as quinine and camphor, are obtained from the bark or wood of certain stems. This shows how closely human life is connected to the biology of the plant stem.

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🖼️ Images & Media (11)
File:Plant nodes c.jpg
Plant nodes c.jpg
File:Polygonum amphibium (4973671699).jpg
Polygonum amphibium (4973671699).jpg
File:Translocation from the source to the sink within the phloem.svg
Translocation from the source to the sink...
File:Illustration of various types of plant stems.png
Illustration of various types of plant stems.png
File:Senecio angulatus stems.jpg
Senecio angulatus stems.jpg
File:Cucurbita_maxima_Zapallo_Plomo_semillería_Costanzi_-_vine_detail_decumbent_shoot_and_tendril.jpg
Cucurbita_maxima_Zapallo_Plomo_semillería_...
File:Labeledstemforposter copy new.jpg
Labeledstemforposter copy new.jpg
File:Royal Palm Trunk.jpg
Royal Palm Trunk.jpg
File:Redwood M D Vaden.jpg
Redwood M D Vaden.jpg
File:Dicksonia antarctica in Nunniong, Australia.jpg
Dicksonia antarctica in Nunniong, Australia.jpg
File:Asparagus produce-1.jpg
Asparagus produce-1.jpg
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