Adventitious, in
botanyBotany, plant science, phytology, or plant biology is a branch of biology and is the scientific study of plant life and development...
, refers to structures that develop in an unusual place, and in
medicineMedicine is the art and science of healing. It encompasses a range of health care practices evolved to maintain and restore health by the prevention and treatment of illness....
, it refers to conditions acquired after birth. This article discusses adventitious
rootIn vascular plants, the root is the organ of a plant that typically lies below the surface of the soil. This is not always the case, however, since a root can also be aerial or aerating . Furthermore, a stem normally occurring below ground is not exceptional either...
s,
budthumb|right|Flower buds have not yet bloomed into a full-size flower.In botany, a bud is an undeveloped or embryonic shoot and normally occurs in the axil of a leaf or at the tip of the stem...
s and
shootShoots are new plant growth, they can include stems, flowering stems with flower buds, leaves. The new growth from seed germination that grows upward is a shoot where leaves will develop...
s, which are very common in
vascular plantVascular plants are those plants that have lignified tissues for conducting water, minerals, and photosynthetic products through the plant. Vascular plants include the ferns, clubmosses, flowering plants, conifers and other gymnosperms...
s.
Adventitious buds and shoots
Adventitious
budthumb|right|Flower buds have not yet bloomed into a full-size flower.In botany, a bud is an undeveloped or embryonic shoot and normally occurs in the axil of a leaf or at the tip of the stem...
s develop from places other than a shoot apical meristem, which occurs at the tip of a stem. They may develop on stems, roots or leaves. Shoot apical meristems produce one or more axillary or lateral buds at each node. When stems produce considerable
secondary growthIn many vascular plants, secondary growth is the result of the activity of the vascular cambium. The latter is a meristem that divides to produce secondary xylem cells on the inside of the meristem and secondary phloem cells on the outside...
, the axillary buds may be destroyed. Adventitious buds may then develop on stems with secondary growth.
Adventitious buds are often formed after the stem is wounded or
prunedPruning is the process of removing certain above-ground elements from a plant; in landscaping this process usually involves removal of diseased, non-productive, or otherwise unwanted portions from a plant. In nature, certain meteorological conditions such as wind, snow or seawater mist can conduct...
. The adventitious buds help to replace lost branches. Adventitious buds and shoots also may develop on mature tree trunks when a shaded trunk is exposed to bright sunlight because surrounding trees are cut down.
RedwoodSequoia sempervirens is the sole living species of the genus Sequoia in the cypress family Cupressaceae . Common names include Coast Redwood and California Redwood...
(
Sequoia sempervirens) trees often develop many adventitious buds on their lower trunks. If the main trunk dies, a new one often sprouts from one of the adventitious buds. Small pieces of redwood trunk are sold as souvenirs termed redwood burls. They are placed in a pan of water, and the adventitious buds sprout to form shoots.
Some plants normally develop adventitious buds on their roots, which can extend quite a distance from the plant. Shoots that develop from adventitious buds on roots are termed
suckersA basal shoot, root sprout, adventitious shoot, water sprout or sucker is a shoot or cane which grows from a bud at the base of a tree or shrub or from its roots. Root suckers may emerge some distance from the originating plant such as in Rhus spp, some Prunus species and Embothrium species...
. They are a type of natural
vegetative reproductionVegetative reproduction is a type of asexual reproduction for plants, and is also called vegetative propagation, vegetative multiplication, or vegetative cloning. It is a process by which new plant "individuals" arise or are obtained without production of seeds or spores...
in many
speciesIn biology, a species is:* a taxonomic rank or* a unit at that rank ....
, e.g. many grasses, quaking aspen and Canada thistle. The Pando quaking aspen grew from one trunk to 47,000 trunks via adventitious bud formation on a single root system.
Some leaves develop adventitious buds, which then form adventitious roots, as part of
vegetative reproductionVegetative reproduction is a type of asexual reproduction for plants, and is also called vegetative propagation, vegetative multiplication, or vegetative cloning. It is a process by which new plant "individuals" arise or are obtained without production of seeds or spores...
; e.g. piggyback plant (
Tolmiea menziesii) and mother-of-thousands (
Kalanchoe daigremontianaKalanchoe daigremontiana syn. Bryophyllum daigremontianum also called Devil's Backbone, Alligator Plant, Mexican Hat Plant or Mother of Thousands is a succulent plant native to Madagascar. This plant is distinguished by its ability to propagate via vegetative propagation...
). The adventitious plantlets then drop off the parent plant and develop as separate
cloneCloning in biology is the process of producing populations of genetically-identical individuals that occurs in nature when organisms such as bacteria, insects or plants reproduce asexually. Cloning in biotechnology refers to processes used to create copies of DNA fragments , cells , or organisms...
s of the parent.
CoppicingCoppicing is a traditional method of woodland management in which young tree stems are repeatedly cut down to near ground level. In subsequent growth years, many new shoots will emerge, and, after a number of years the coppiced tree, or stool, is ready to be harvested, and the cycle begins again...
is the practice of cutting
treeA tree is a perennial woody plant. It is most often defined as a woody plant that has many secondary branches supported clear of the ground on a single main stem or trunk with clear apical dominance. A minimum height specification at maturity is cited by some authors, varying from 3 m to...
stems to the ground to promote rapid growth of adventitious shoots. It is traditionally used to produce poles, fence material or
firewoodFirewood is any wood like material that is gathered and used for fuel. Generally, firewood is not highly processed and is in some sort of recognizable log or branch form....
. It is also practiced for
biomassBiomass, a renewable energy source, is biological material derived from living, or recently living organisms, such as wood, waste, and alcohol fuels. Biomass is commonly plant matter grown to generate electricity or produce heat. For example, forest residues , yard clippings and wood chips may be...
crops grown for fuel, such as
poplarPopulus is a genus of 25–35 species of deciduous flowering plants in the family Salicaceae, native to most of the Northern Hemisphere. English names variously applied to different species include poplar, aspen, and cottonwood....
or willow.
Location of origin
Adventitious roots and buds usually develop near the existing vascular tissues so they can connect to the
xylemIn vascular plants, xylem is one of the two types of transport tissue, phloem being the other. The word "xylem" is derived from classical Greek ξυλον , "wood", and indeed the best-known xylem tissue is wood, though it is found throughout the plant...
and
phloemIn vascular plants, phloem is the living tissue that carries organic nutrients , particularly sucrose, a sugar, to all parts of the plant where needed. In trees, the phloem is the innermost layer of the bark, hence the name, derived from the Greek word "bark"...
. However, the exact location varies greatly. In young stems, adventitious roots often form from
parenchymaParenchyma is a term used to describe a bulk of a substance. It is used in different ways in animals and in plants.The term is New Latin, from Greek parenkhuma, visceral flesh, from parenkhein, to pour in beside : para-, beside + en-, in + khein, to pour.- In animals :The parenchyma are the...
between the
vascular bundleA vascular bundle is a part of the transport system in vascular plants. The transport itself happens in vascular tissue, which exists in two forms: xylem and phloem. Both these tissues are present in a vascular bundle, which in addition will include supporting and protective tissues...
s. In stems with secondary growth, adventitious roots often originate in phloem parenchyma near the
vascular cambiumThe vascular cambium is a lateral meristem in the vascular tissue of plants. The vascular cambium is the source of both the secondary xylem and the secondary phloem , and is located between these tissues in the stem and root...
. In stem cuttings, adventitious roots sometimes also originate in the
callusA callus is an especially toughened area of skin which has become relatively thick and hard in response to repeated friction, pressure, or other irritation. Rubbing that is too frequent or forceful will cause blisters rather than allow calluses to form. Since repeated contact is required,...
cells that form at the cut surface. Leaf cuttings of the
CrassulaCrassula is a large genus of succulent plants containing many species, including the popular Jade Plant, Crassula ovata. They are native to many parts of the globe, but cultivated varieties are almost exclusively from the Eastern Cape of South Africa....
form adventitious roots in the epidermis.
Modification of adventitious root
Tuberous roots are without any definite shape; example:
sweet PotatoThe sweet potato is a dicotyledonous plant that belongs to the family Convolvulaceae. Amongst the approximately 50 genera and more than 1,000 species of this family, only I. batatas is a crop plant whose large, starchy, sweet tasting tuberous roots are an important root vegetable...
.
Fasciculated root (tuberous root) occur in clusters at the base of the stem; example:
asparagusAsparagus officinalis is a flowering plant species in the genus Asparagus from which the vegetable known as asparagus is obtained. It is native to most of Europe, northern Africa and western Asia...
,
dahliaDahlia is a genus of bushy, tuberous, perennial plants native to Mexico, Central America, and Colombia. There are at least 36 species of dahlia. Dahlia hybrids are commonly grown as garden plants. The Aztecs gathered and cultivated the dahlia for food, ceremonies, as well as decorative purposes,...
.
Nodulose roots become swollen near the tips; example:
turmericTurmeric is a rhizomatous herbaceous perennial plant of the ginger family, Zingiberaceae. It is native to tropical South Asia and needs temperatures between 20°C and 30°C, and a considerable amount of annual rainfall to thrive...
.
Stilt roots arise from the first few nodes of the stem. These penetrate obliquely down in to the soil and give support to the plant; example:
maizeMaize , is a herbaceous plant domesticated in Mesoamerica and subsequently spread throughout the American continents...
,
sugarcaneSugarcane, or sugar cane, is any of six to thirty-seven species of tall perennial grasses of the genus Saccharum . Native to warm temperate to tropical regions of Asia, they have stout, jointed, fibrous stalks that are rich in sugar, and measure two to six meters tall...
.
Prop roots give mechanical support to the aerial branches. The lateral branches grow vertically downward into the soil and acts as pillars; example:
banyanA banyan is a fig that starts its life as an epiphyte when its seeds germinate in the cracks and crevices on a host tree...
.
Vegetative propagation
Adventitious roots and buds are very important when people propagate plants via cuttings,
layeringLayering is a means of plant propagation in which a portion of an aerial stem grow roots while still attached to the parent plant and then detaches as an independent plant. Layering has evolved as a common means of vegetative propagation of numerous species in natural environments...
,
tissue culturePlant tissue culture is a practice used to propagate plants under sterile conditions, often to produce clones of a plant. Different techniques in plant tissue culture may offer certain advantages over traditional methods of propagation, including:...
. Plant hormones, termed
auxinAuxins are a class of plant growth substance and morphogens . Auxins have an essential role in coordination of many growth and behavioral processes in the plant life cycle...
s, are often applied to stem,
shootShoots are new plant growth, they can include stems, flowering stems with flower buds, leaves. The new growth from seed germination that grows upward is a shoot where leaves will develop...
or
leafIn botany, a leaf is an above-ground plant organ specialized for photosynthesis. For this purpose, a leaf is typically flat and thin. There is continued debate about whether the flatness of leaves evolved to expose the chloroplasts to more light or to increase the absorption of carbon dioxide. In...
cuttings to promote adventitious root formation, e.g. African violet and
sedumSedum is the large stonecrop genus of the Crassulaceae, representing about 400 species of leaf succulents, found throughout the northern hemisphere, varying from annual and creeping herbs to shrubs. The plants have water-storing leaves. The flowers usually have five petals, seldom four or six...
leaves and shoots of
poinsettiaEuphorbia pulcherrima, commonly known as poinsettia, is a species of flowering plant indigenous to Mexico and Guatemala.The name "poinsettia" is after Joel Roberts Poinsett, the first United States Minister to Mexico, who introduced the plant into the US in 1828.-Christmas tradition:In Nahuatl, the...
and
coleusSolenostemon is a genus of perennial plants, native to tropical Africa, Asia, Australia, the East Indies, the Malay Archipelago, and the Philippines...
. Propagation via root cuttings requires adventitious bud formation, e.g. in
horseradishHorseradish is a perennial plant of the Brassicaceae family, which also includes mustard, wasabi, broccoli, and cabbages. The plant is probably native to southeastern Europe and western Asia, but is popular around the world today...
and
appleThe apple is the pomaceous fruit of the apple tree, species Malus domestica in the rose family Rosaceae. It is one of the most widely cultivated tree fruits...
. In layering, adventitious roots are formed on aerial stems before the stem section is removed to make a new plant. Large houseplants are often propagated by air layering. Adventitious roots and buds must develop in tissue culture propagation of plants.