Woody plant

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A section of rosemary stem, an example of a woody plant, showing a typical wood structure. RosmaryStem SatCrop BgSub.jpg
A section of rosemary stem, an example of a woody plant, showing a typical wood structure.

A woody plant is a plant that produces wood as its structural tissue and thus has a hard stem. In cold climates, woody plants further survive winter or dry season above ground, as opposite to herbaceous plants that die back to the ground until spring. [1]

Contents

Characteristics

Woody plants are usually either trees, shrubs, or lianas. These are usually perennial plants whose stems and larger roots are reinforced with wood produced from secondary xylem. The main stem, larger branches, and roots of these plants are usually covered by a layer of bark. Wood is a structural tissue that allows woody plants to grow from above ground stems year after year, thus making some woody plants the largest and tallest terrestrial plants.

Woody plants, like herbaceous perennials, typically have a dormant period of the year when growth does not take place, in colder climates due to freezing temperatures and lack of daylight during the winter months, in subtropical and tropical climates due to the dry season when precipitation becomes minimal. The dormant period will be accompanied by shedding of leaves if the plant is deciduous. Evergreen plants do not lose all their leaves at once (they instead shed them gradually over the growing season), however growth virtually halts during the dormant season. Many woody plants native to subtropical regions and nearly all native to the tropics are evergreen due to year-round warm temperatures.

During the fall months, each stem in a deciduous plant cuts off the flow of nutrients and water to the leaves. This causes them to change colors as the chlorophyll in the leaves breaks down. Special cells are formed that sever the connection between the leaf and stem, so that it will easily detach. Evergreen plants do not shed their leaves and merely go into a state of low activity during the dormant season. During spring, the roots begin sending nutrients back up to the canopy.

When the growing season resumes, either with warm weather or the wet season, the plant will break bud by sending out new leaf or flower growth. This is accompanied by growth of new stems from buds on the previous season's wood. In colder climates, most stem growth occurs during spring and early summer. When the dormant season begins, the new growth hardens off and becomes woody. Once this happens, the stem will never grow in length again, however it will keep expanding in diameter for the rest of the plant's life.

Most woody plants native to colder climates have distinct growth rings produced by each year's production of new vascular tissue. Only the outer handful of rings contain living tissue (the cambium, xylem, phloem, and sapwood). Inner layers have heartwood, dead tissue that serves merely as structural support.

Growth

Winter buds on Cercidiphyllum japonicum. Cercidiphyllum japonicum 03-02.19.jpg
Winter buds on Cercidiphyllum japonicum.

Stem growth primarily occurs out of the terminal bud on the tip of the stem. Buds on the sides of the stem are suppressed by the terminal bud and produce less growth, unless it is removed by human or natural action. Without a terminal bud, the side buds will have nothing to suppress them and begin rapidly sending out growth, if cut during spring. By late summer and early autumn, most active growth for the season has ceased and pruning a stem will result in little or no new growth. Winter buds are formed when the dormant season begins. Depending on the plant, these buds contain either new leaf growth, new flowers, or both.

Terminal buds have a stronger dominance on conifers than broadleaf plants, thus conifers will normally grow a single straight trunk without forking or large side or lateral branches.

As a woody plant grows, it will often lose lower leaves and branches as they become shaded out by the canopy. If a given stem is producing an insufficient amount of energy for the plant, the roots will "abort" it by cutting off the flow of water and nutrients, causing it to gradually die.

Below ground, the root system expands each growing season in much the same manner as the stems. The roots grow in length and send out smaller lateral roots. At the end of the growing season, the newly grown roots become woody and cease future length expansion, but will continue to expand in diameter. However, unlike the above-ground portion of the plant, the root system continues to grow, although at a slower rate, throughout the dormant season. In cold-weather climates, root growth will continue as long as temperatures are above 36 °F (2 °C).

Tissue composition

Wood is primarily composed of xylem cells with cell walls made of cellulose and lignin. Xylem is a vascular tissue which moves water and nutrients from the roots to the leaves. Most woody plants form new layers of woody tissue each year, and so increase their stem diameter from year to year, with new wood deposited on the inner side of a vascular cambium layer located immediately beneath the bark. However, in some monocotyledons such as palms and dracaenas, the wood is formed in bundles scattered through the interior of the trunk. Stem diameter increases continuously throughout the growing season and halts during the dormant period. [2]

Under specific conditions, woody plants may decay or may in time become petrified wood.

Symbol

The symbol for a woody plant, based on Species Plantarum by Linnaeus is Saturn symbol.svg , which is also the astronomical symbol for the planet Saturn. [3]

See also

Related Research Articles

Bud Immature or embryonic shoot

In botany, a bud is an undeveloped or embryonic shoot and normally occurs in the axil of a leaf or at the tip of a stem. Once formed, a bud may remain for some time in a dormant condition, or it may form a shoot immediately. Buds may be specialized to develop flowers or short shoots or may have the potential for general shoot development. The term bud is also used in zoology, where it refers to an outgrowth from the body which can develop into a new individual.

Xylem Water transport tissue in vascular plants

Xylem is one of the two types of transport tissue in vascular plants, the other being phloem. The basic function of xylem is to transport water from roots to stems and leaves, but it also transports nutrients. The word xylem is derived from the Ancient Greek word ξύλον (xylon), meaning "wood"; the best-known xylem tissue is wood, though it is found throughout a plant. The term was introduced by Carl Nägeli in 1858.

Root Part of a plant

In vascular plants, the roots are the organs of a plant that are modified to provide anchorage for the plant and take in water and nutrients into the plant body, which allows plants to grow taller and faster. They are most often below the surface of the soil, but roots can also be aerial or aerating, that is, growing up above the ground or especially above water.

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Bark is the outermost layers of stems and roots of woody plants. Plants with bark include trees, woody vines, and shrubs. Bark refers to all the tissues outside the vascular cambium and is a nontechnical term. It overlays the wood and consists of the inner bark and the outer bark. The inner bark, which in older stems is living tissue, includes the innermost layer of the periderm. The outer bark on older stems includes the dead tissue on the surface of the stems, along with parts of the outermost periderm and all the tissues on the outer side of the periderm. The outer bark on trees which lies external to the living periderm is also called the rhytidome.

Vascular cambium Main growth tissue in the stems, roots of plants

The vascular cambium is the main growth tissue in the stems and roots of many plants, specifically in dicots such as buttercups and oak trees, gymnosperms such as pine trees, as well as in certain other vascular plants. It produces secondary xylem inwards, towards the pith, and secondary phloem outwards, towards the bark.

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Perennial plant Plant that lives for more than two years

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Vascular tissue Conducting tissue in vascular plants

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Secondary growth Type of growth in plants

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Lepidodendrales Extinct order of vascular tree-like plants

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Tree Perennial woody plant with elongated trunk

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Herbchronology

Herbchronology is the analysis of annual growth rings in the secondary root xylem of perennial herbaceous plants. While leaves and stems of perennial herbs die down at the end of the growing season the root often persists for many years or even the entire life. Perennial herb species belonging to the dicotyledon group are characterized by secondary growth, which shows as a new growth ring added each year to persistent roots. About two thirds of all perennial dicotyledonous herb species with a persistent root that grow in the strongly seasonal zone of the northern hemisphere show at least fairly clear annual growth rings.

Cambium

A cambium, in plants, is a tissue layer that provides partially undifferentiated cells for plant growth. It is found in the area between xylem and phloem. A cambium can also be defined as a cellular plant tissue from which phloem, xylem, or cork grows by division, resulting in secondary thickening. It forms parallel rows of cells, which result in secondary tissues.

References

  1. "Learn About Examples of Woody Plants". The Spruce. Retrieved 2020-09-17.
  2. Chase, Mark W. (2004). "Monocot relationships: an overview". Am. J. Bot. 91 (10): 1645–1655. doi: 10.3732/ajb.91.10.1645 . PMID   21652314.
  3. Stearn, William T. (1992) [1966]. Botanical Latin (Fourth ed.). Portland: Timber Press. ISBN   0881923214.