A woody plant is a plant that produces wood as its structural tissue and thus has a hard stem. [1] In cold climates, woody plants further survive winter or dry season above ground, as opposed to herbaceous plants that die back to the ground until spring. [2]
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Woody plants are usually 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.
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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 2 °C (36 °F).
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. [3]
The symbol for a woody plant, based on Species Plantarum by Linnaeus is 
, which is also the astronomical symbol for the planet Saturn. [4]
Xylem is one of the two types of transport tissue in vascular plants, the other being phloem. The basic function of the 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.
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.
In biology, tissue is a historically derived biological organizational level between cells and a complete organ. A tissue is therefore often thought of as an assembly of similar cells and their extracellular matrix from the same embryonic origin that together carry out a specific function. Organs are then formed by the functional grouping together of multiple tissues.
Bark is the outermost layer 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.
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.
Herbaceous plants are vascular plants that have no persistent woody stems above ground. This broad category of plants includes many perennials, and nearly all annuals and biennials.
In botany, the trunk is the stem and main wooden axis of a tree, which is an important feature in tree identification, and which often differs markedly from the bottom of the trunk to the top, depending on the species.
A perennial plant or simply perennial is a plant that lives more than two years. The term is often used to differentiate a plant from shorter-lived annuals and biennials. The term is also widely used to distinguish plants with little or no woody growth from trees and shrubs, which are also technically perennials.Notably, it is estimated that 94% of plant species fall under the category of perennials, underscoring the prevalence of plants with lifespans exceeding two years in the botanical world
Lepidodendron is an extinct genus of primitive lycopodian vascular plants belonging the order Lepidodendrales. It is well preserved and common in the fossil record. Like other Lepidodendrales, species of Lepidodendron grew as large-tree-like plants in wetland coal forest environments. They sometimes reached heights of 50 metres, and the trunks were often over 1 m (3.3 ft) in diameter. They are often known as "scale trees", due to their bark having been covered in diamond shaped leaf-bases, from which leaves grew during earlier stages of growth. They thrived during the Carboniferous Period, and persisted until the end of the Permian around 252 million years ago. Sometimes erroneously called "giant club mosses", the genus was actually more closely related to modern quillworts than to modern club mosses. Within the form classification system used within paleobotany, Lepidodendron is both used for the whole plant as well as specifically the stems and leaves.
Girdling, also called ring-barking, is the circumferential removal or injury of the bark of a branch or trunk of a woody plant. Girdling prevents the tree from sending nutrients from its foliage to its roots, resulting in the death of the tree over time, and can also prevent flow of nutrients in the other direction depending on how much of the xylem is removed. A branch completely girdled will fail and when the main trunk of a tree is girdled, the entire tree will die, if it cannot regrow from above to bridge the wound. Human practices of girdling include forestry, horticulture, and vandalism. Foresters use the practice of girdling to thin forests. Extensive cankers caused by certain fungi, bacteria or viruses can girdle a trunk or limb. Animals such as rodents will girdle trees by feeding on outer bark, often during winter under snow. Girdling can also be caused by herbivorous mammals feeding on plant bark and by birds and insects, both of which can effectively girdle a tree by boring rows of adjacent holes.
Vascular tissue is a complex conducting tissue, formed of more than one cell type, found in vascular plants. The primary components of vascular tissue are the xylem and phloem. These two tissues transport fluid and nutrients internally. There are also two meristems associated with vascular tissue: the vascular cambium and the cork cambium. All the vascular tissues within a particular plant together constitute the vascular tissue system of that plant.
In botany, secondary growth is the growth that results from cell division in the cambia or lateral meristems and that causes the stems and roots to thicken, while primary growth is growth that occurs as a result of cell division at the tips of stems and roots, causing them to elongate, and gives rise to primary tissue. Secondary growth occurs in most seed plants, but monocots usually lack secondary growth. If they do have secondary growth, it differs from the typical pattern of other seed plants.
This page provides a glossary of plant morphology. Botanists and other biologists who study plant morphology use a number of different terms to classify and identify plant organs and parts that can be observed using no more than a handheld magnifying lens. This page provides help in understanding the numerous other pages describing plants by their various taxa. The accompanying page—Plant morphology—provides an overview of the science of the external form of plants. There is also an alphabetical list: Glossary of botanical terms. In contrast, this page deals with botanical terms in a systematic manner, with some illustrations, and organized by plant anatomy and function in plant physiology.
Grafting or graftage is a horticultural technique whereby tissues of plants are joined so as to continue their growth together. The upper part of the combined plant is called the scion while the lower part is called the rootstock. The success of this joining requires that the vascular tissues grow together. The natural equivalent of this process is inosculation. The technique is most commonly used in asexual propagation of commercially grown plants for the horticultural and agricultural trades. The scion is typically joined to the rootstock at the soil line; however, top work grafting may occur far above this line, leaving an understock consisting of the lower part of the trunk and the root system.
Important structures in plant development are buds, shoots, roots, leaves, and flowers; plants produce these tissues and structures throughout their life from meristems located at the tips of organs, or between mature tissues. Thus, a living plant always has embryonic tissues. By contrast, an animal embryo will very early produce all of the body parts that it will ever have in its life. When the animal is born, it has all its body parts and from that point will only grow larger and more mature. However, both plants and animals pass through a phylotypic stage that evolved independently and that causes a developmental constraint limiting morphological diversification.
Lepidodendrales or arborescent lycophytes are an extinct order of primitive, vascular, heterosporous, arborescent (tree-like) plants belonging to Lycopodiopsida. Members of Lepidodendrales are the best understood of the fossil lycopsids due to the vast diversity of Lepidodendrales specimens and the diversity in which they were preserved; the extensive distribution of Lepidodendrales specimens as well as their well-preservedness lends paleobotanists exceptionally detailed knowledge of the coal-swamp giants’ reproductive biology, vegetative development, and role in their paleoecosystem. The defining characteristics of the Lepidodendrales are their secondary xylem, extensive periderm development, three-zoned cortex, rootlike appendages known as stigmarian rootlets arranged in a spiralling pattern, and megasporangium each containing a single functional megaspore that germinates inside the sporangium. Many of these different plant organs have been assigned both generic and specific names as relatively few have been found organically attached to each other. Some specimens have been discovered which indicate heights of 40 and even 50 meters and diameters of over 2 meters at the base. The massive trunks of some species branched profusely, producing large crowns of leafy twigs; though some leaves were up to 1 meter long, most were much shorter, and when leaves dropped from branches their conspicuous leaf bases remained on the surface of branches. Strobili could be found at the tips of distal branches or in an area at the top of the main trunk. The underground organs of Lepidodendrales typically consisted of dichotomizing axes bearing helically arranged, lateral appendages serving an equivalent function to roots. Sometimes called "giant club mosses", they are believed to be more closely related to extant quillworts based on xylem, although fossil specimens of extinct Selaginellales from the Late Carboniferous also had secondary xylem.
A stem is one 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. The stem can also be called halm or haulm or culms.
In botany, a tree is a perennial plant with an elongated stem, or trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, including only woody plants with secondary growth, plants that are usable as lumber or plants above a specified height. In wider definitions, the taller palms, tree ferns, bananas, and bamboos are also trees.
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.
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.
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