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Stem showing internode and nodes plus leaf petioles
This above-ground stem of Polygonum has lost its leaves, but is producing adventitious roots from the nodes.
Xylem and Phloem

A stem is on of two main structural axes of a vascular plant, the other being the root. It supports leaves, flowers and fruits, transports water and dissolved substances between the roots and the shoots in the xylem and phloem, photosynthesis takes place here, stores nutrients, and produces new living tissue.[1] The stem can also be called halm or haulm or culms.

The stem is normally divided into nodes and internodes:[2]

The term "shoots" is often confused with "stems"; "shoots" generally refers to new fresh plant growth, including both stems and other structures like leaves or flowers.[2]

In most plants, stems are located above the soil surface, but some plants have underground stems.

Stems have several main functions:[3]

Stems have two pipe-like tissues called xylem and phloem. The xylem tissue arises from the cell facing inside and transports water by the action of transpiration pull, capillary action, and root pressure. The phloem tissue arises from the cell facing outside and consists of sieve tubes and their companion cells. The function of phloem tissue is to distribute food from photosynthetic tissue to other tissues. The two tissues are separated by cambium, a tissue that divides to form xylem or phloem cells.

Specialized terms

Stems are often specialized for storage, asexual reproduction, protection, or photosynthesis, including the following:

Climbing stem of Senecio angulatus.
Decumbent stem in Cucurbita maxima.

Stem structure

See also: Stele (biology)

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Flax stem cross-section, showing locations of underlying tissues. Ep = epidermis; C = cortex; BF = bast fibres; P = phloem; X = xylem; Pi = pith

Stem usually consist of three tissues: dermal tissue, ground tissue, and vascular tissue.[5]

Dermal tissue covers the outer surface of the stem and usually functions to protect the stem tissue, and control gas exchange.[6] The predominant cells of dermal tissue are epidermal cells.[7] The dermal tissue of aquatic plants stems may lack the waterproofing found in aerial stems.

Ground tissue usually consists mainly of parenchyma cells and fills in around the vascular tissue. It sometimes functions in photosynthesis. Most or all ground tissue may be lost in woody stems.

Vascular tissue provides long distance transport and structural support. The arrangement of the vascular tissues varies widely among plant species.

Dicot stems

Dicot stems with primary growth have pith in the center, with vascular bundles forming a distinct ring visible when the stem is viewed in cross section. The outside of the stem is covered with an epidermis, which is covered by a waterproof cuticle. The epidermis also may contain stomata for gas exchange and multicellular stem hairs called trichomes. A cortex consisting of hypodermis (collenchyma cells) and endodermis (starch containing cells) is present above the pericycle and vascular bundles.

Woody dicots and many nonwoody dicots have secondary growth originating from their lateral or secondary meristems: the vascular cambium and the cork cambium or phellogen. The vascular cambium forms between the xylem and phloem in the vascular bundles and connects to form a continuous cylinder. The vascular cambium cells divide to produce secondary xylem to the inside and secondary phloem to the outside. As the stem increases in diameter due to production of secondary xylem and secondary phloem, the cortex and epidermis are eventually destroyed. Before the cortex is destroyed, a cork cambium develops there. The cork cambium divides to produce waterproof cork cells externally and sometimes phelloderm cells internally. Those three tissues form the periderm, which replaces the epidermis in function. Areas of loosely packed cells in the periderm that function in gas exchange are called lenticels.

Secondary xylem is commercially important as wood. The seasonal variation in growth from the vascular cambium is what creates yearly tree rings in temperate climates. Tree rings are the basis of dendrochronology, which dates wooden objects and associated artifacts. Dendroclimatology is the use of tree rings as a record of past climates. The aerial stem of an adult tree is called a trunk. The dead, usually darker inner wood of a large diameter trunk is termed the heartwood and is the result of tylosis. The outer, living wood is termed the sapwood.

Monocot stems

Stems of two Roystonea regia palms showing characteristic bulge, leaf scars and fibrous roots, Kolkata, India

Vascular bundles are present throughout the monocot stem, although concentrated towards the outside. This differs from the dicot stem that has a ring of vascular bundles and often none in the center. The shoot apex in monocot stems is more elongated. Leaf sheathes grow up around it, protecting it. This is true to some extent of almost all monocots. Monocots rarely produce secondary growth and are therefore seldom woody, with palms and bamboo being notable exceptions. However, many monocot stems increase in diameter via anomalous secondary growth.

Gymnosperm stems

All gymnosperms are woody plants. Their stems are similar in structure to woody dicots except that most gymnosperms produce only tracheids in their xylem, not the vessels found in dicots. Gymnosperm wood also often contains resin ducts. Woody dicots are called hardwoods, e.g. oak, maple and walnut. In contrast, softwoods are gymnosperms, such as pine, spruce and fir.

Fern stems

Most ferns have rhizomes with no vertical stem. The exception is tree ferns, which have vertical stems that can grow up to about 20 metres. The stem anatomy of ferns is more complicated than that of dicots because fern stems often have one or more leaf gaps in cross section. A leaf gap is where the vascular tissue branches off to a frond. In cross section, the vascular tissue does not form a complete cylinder where a leaf gap occurs. Fern stems may have solenosteles or dictyosteles or variations of them. Many fern stems have phloem tissue on both sides of the xylem in cross-section.

Relation to xenobiotics

Foreign chemicals such as air pollutants,[8] herbicides and pesticides can damage stem structures.

Economic importance

White and green asparagus – crispy stems are the edible parts of this vegetable

There are thousands of species whose stems have economic uses. Stems provide a few major staple crops such as potato and taro. Sugarcane stems are a major source of sugar. Maple sugar is obtained from trunks of maple trees. Vegetables from stems are asparagus, bamboo shoots, cactus pads or nopalitos, kohlrabi, and water chestnut. The spice, cinnamon is bark from a tree trunk. Gum arabic is an important food additive obtained from the trunks of Acacia senegal trees. Chicle, the main ingredient in chewing gum, is obtained from trunks of the chicle tree.

Medicines obtained from stems include quinine from the bark of cinchona trees, camphor distilled from wood of a tree in the same genus that provides cinnamon, and the muscle relaxant curare from the bark of tropical vines.

Wood is used in thousands of ways; it can be used to create buildings, furniture, boats, airplanes, wagons, car parts, musical instruments, sports equipment, railroad ties, utility poles, fence posts, pilings, toothpicks, matches, plywood, coffins, shingles, barrel staves, toys, tool handles, picture frames, veneer, charcoal and firewood. Wood pulp is widely used to make paper, paperboard, cellulose sponges, cellophane and some important plastics and textiles, such as cellulose acetate and rayon. Bamboo stems also have hundreds of uses, including in paper, buildings, furniture, boats, musical instruments, fishing poles, water pipes, plant stakes, and scaffolding. Trunks of palms and tree ferns are often used for building. Stems of reed are an important building material for use in thatching in some areas.

Tannins used for tanning leather are obtained from the wood of certain trees, such as quebracho. Cork is obtained from the bark of the cork oak. Rubber is obtained from the trunks of Hevea brasiliensis. Rattan, used for furniture and baskets, is made from the stems of tropical vining palms. Bast fibers for textiles and rope are obtained from stems of plants like flax, hemp, jute and ramie. The earliest known paper was obtained from the stems of papyrus by the ancient Egyptians.

Amber is fossilized sap from tree trunks; it is used for jewelry and may contain preserved animals. Resins from conifer wood are used to produce turpentine and rosin. Tree bark is often used as a mulch and in growing media for container plants. It also can become the natural habitat of lichens.

Some ornamental plants are grown mainly for their attractive stems, e.g.:

See also


  1. ^ Plant Stems: Physiology and Functional Morphology. Elsevier. 1995-07-19. ISBN 978-0-08-053908-9.
  2. ^ a b c d Britannica Lessons Class VI Science The Living World. Popular Prakashan. 2002. ISBN 9788171549719, 8171549713. ((cite book)): Check |isbn= value: invalid character (help)
  3. ^ Raven, Peter H., Ray Franklin Evert, and Helena Curtis (1981). Biology of Plants. New York: Worth Publishers. ISBN 0-87901-132-7.
  4. ^ Goebel, K.E.v. (1969) [1905]. Organography of plants, especially of the Archegoniatae and Spermaphyta. New York: Hofner publishing company.
  5. ^ "Stem Anatomy". LibreTexts Biology. 11 May 2024. Retrieved 11 May 2024.
  6. ^ "Stems - Stem Anatomy". LibreTexts Biology. 11 June 2024. Retrieved 11 June 2024.
  7. ^ "Stems - Stem Anatomy". LibreTexts Biology. 11 June 2024. Retrieved 11 June 2024.
  8. ^ C. Michael Hogan. 2010. "Abiotic factor". Encyclopedia of Earth. Emily Monosson and C. Cleveland, eds. National Council for Science and the Environment Archived 2013-06-08 at the Wayback Machine. Washington, D.C.

Further reading