Variegation
Encyclopedia
Variegation is the appearance of differently coloured zones in the leaves
, and sometimes the stems
, of plant
s. This may be due to a number of causes. Some variegation is attractive and ornamental and gardeners tend to preserve these.
The term is also sometimes used to refer to colour zonation in flower
s, mineral
s, and the skin, fur, feathers or scales of animals.
, with more than one type of genetic makeup in their tissues. A lack of chlorophyll
producing tissue in some tissues causes variegation with white or yellow coloured zones on the leaf, contrasting with the usual green tissue. It is due to some of the plant’s meristem
atic tissue losing the ability to produce chloroplast
s, so that the tissue it produces is no longer green.
In a common type of such variegation, the part of the meristem that produces epidermal tissue loses the ability to produce chloroplasts. The margins of leaves may be composed only of cells derived from this merismatic tissue. Hence, this marginal tissue is white or yellow, rather than green. There are several other types of such variegation, depending on the tissues that have been affected, and their relationship to each other. Variegation may be consistent and symmetric in appearance throughout the whole plant, or it may be quite random in location. In some plants, entire branches or stems including the leaves may be variegated. The variegation in some forms is unstable. The extent and nature of the variegation can vary, and sometimes the plant will return to the green form. In others it is stable and does not change under normal conditions.
Because the variegation is due to the presence of two kinds of plant tissue, propagating the plant must be by a vegetative method of propagation that preserves both types of tissue in relation to each other. Typically, stem cuttings, bud and stem grafting
, and other propagation methods that results in growth from leaf axil buds will preserve variegation. Cuttings with complete variegation may be difficult if not impossible to propagate. Root cuttings will not usually preserve variegation, since the new stem tissue is derived from a particular tissue type within the root.
As these plants have some of their tissue unable to carry out photosynthesis
, the plant will be weaker than the plain green plant. They should generally be expected to die out in nature and their only real source of survival is through cultivation.
Some variegation is due to visual effects due to reflection
of light from the leaf surface. This can happen when an air layer is located just under the epidermis
resulting in a white or silvery reflection. It is sometimes called blister variegation.
Pilea
(aluminum plant) is an example of a house plant that shows this effect. Leaves of most Cyclamen
species show such patterned variegation, varying between plants, but consistent within each plant.
Another type of reflective variegation is caused by hairs on parts of the leaf, which may be coloured differently from the leaf. This is found in various Begonia
species and garden hybrids.
Sometimes venal variegation occurs – the veins of the leaf are picked out in white or yellow. This is due to lack of green tissue above the veins. It can be seen in some aroids.
The blessed milk thistle, Silybum marianum, is a plant in which another type of venal variegation occurs, but in this case it is due to a blister variegation occurring along the veins.
by other pigments, such as anthocyanin
s. This often extends to the whole leaf, causing it to be reddish or purplish. On some plants however, consistent zonal markings occur; such as on some clover
s, bromeliads
, certain Pelargonium
and Oxalis
species. On others, such as the commonly grown forms of Coleus
, the variegation can vary widely within a population.
infections may cause patterning to appear on the leaf surface. The patterning is often characteristic of the infection. Examples are the mosaic viruses, which produce a mosaic-type effect on the leaf surface or the citrus variegation virus
(CVV). Hosta Virus X (HVX)Hosta Library: HVX has caused such dramatic and attractive mosaic-type variegations that, when the disease was new to the United States, affected plants were mistakenly thought to be new mutations and were registered as new cultivars.HVX-Infected Cultivars in the Marketplace
While these diseases are usually serious enough that the gardener would not grow affected plants, there are a few affected plants that can survive indefinitely, and are attactive enough to be grown for ornament; e.g. some variegated Abutilon
varieties.
Nutrient
deficiency symptoms may cause a temporary or variable yellowing in specific zones on the leaf. Iron
and magnesium
deficiencies are common causes of this.
's Variegated Plant Special Interest Group in the UK. Several gardening books which deal exclusively with variegated plants are available.
Leaf
A leaf is an organ of a vascular plant, as defined in botanical terms, and in particular in plant morphology. Foliage is a mass noun that refers to leaves as a feature of plants....
, and sometimes the stems
Plant stem
A stem is one of two main structural axes of a vascular plant. The stem is normally divided into nodes and internodes, the nodes hold buds which grow into one or more leaves, inflorescence , conifer cones, roots, other stems etc. The internodes distance one node from another...
, of plant
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...
s. This may be due to a number of causes. Some variegation is attractive and ornamental and gardeners tend to preserve these.
The term is also sometimes used to refer to colour zonation in flower
Flower
A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants . The biological function of a flower is to effect reproduction, usually by providing a mechanism for the union of sperm with eggs...
s, mineral
Mineral
A mineral is a naturally occurring solid chemical substance formed through biogeochemical processes, having characteristic chemical composition, highly ordered atomic structure, and specific physical properties. By comparison, a rock is an aggregate of minerals and/or mineraloids and does not...
s, and the skin, fur, feathers or scales of animals.
Chimeral
Plants bearing such variegation are chimerasChimera (plant)
Chimeras in botany are usually single organisms composed of two genetically different types of tissue. They occur in plants, on the same general basis as with animal chimeras...
, with more than one type of genetic makeup in their tissues. A lack of chlorophyll
Chlorophyll
Chlorophyll is a green pigment found in almost all plants, algae, and cyanobacteria. Its name is derived from the Greek words χλωρος, chloros and φύλλον, phyllon . Chlorophyll is an extremely important biomolecule, critical in photosynthesis, which allows plants to obtain energy from light...
producing tissue in some tissues causes variegation with white or yellow coloured zones on the leaf, contrasting with the usual green tissue. It is due to some of the plant’s meristem
Meristem
A meristem is the tissue in most plants consisting of undifferentiated cells , found in zones of the plant where growth can take place....
atic tissue losing the ability to produce chloroplast
Chloroplast
Chloroplasts are organelles found in plant cells and other eukaryotic organisms that conduct photosynthesis. Chloroplasts capture light energy to conserve free energy in the form of ATP and reduce NADP to NADPH through a complex set of processes called photosynthesis.Chloroplasts are green...
s, so that the tissue it produces is no longer green.
In a common type of such variegation, the part of the meristem that produces epidermal tissue loses the ability to produce chloroplasts. The margins of leaves may be composed only of cells derived from this merismatic tissue. Hence, this marginal tissue is white or yellow, rather than green. There are several other types of such variegation, depending on the tissues that have been affected, and their relationship to each other. Variegation may be consistent and symmetric in appearance throughout the whole plant, or it may be quite random in location. In some plants, entire branches or stems including the leaves may be variegated. The variegation in some forms is unstable. The extent and nature of the variegation can vary, and sometimes the plant will return to the green form. In others it is stable and does not change under normal conditions.
Because the variegation is due to the presence of two kinds of plant tissue, propagating the plant must be by a vegetative method of propagation that preserves both types of tissue in relation to each other. Typically, stem cuttings, bud and stem grafting
Grafting
Grafting is a horticultural technique whereby tissues from one plant are inserted into those of another so that the two sets of vascular tissues may join together. This vascular joining is called inosculation...
, and other propagation methods that results in growth from leaf axil buds will preserve variegation. Cuttings with complete variegation may be difficult if not impossible to propagate. Root cuttings will not usually preserve variegation, since the new stem tissue is derived from a particular tissue type within the root.
As these plants have some of their tissue unable to carry out photosynthesis
Photosynthesis
Photosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...
, the plant will be weaker than the plain green plant. They should generally be expected to die out in nature and their only real source of survival is through cultivation.
Reflective
Reflection (physics)
Reflection is the change in direction of a wavefront at an interface between two differentmedia so that the wavefront returns into the medium from which it originated. Common examples include the reflection of light, sound and water waves...
of light from the leaf surface. This can happen when an air layer is located just under the epidermis
Epidermis (botany)
The epidermis is a single-layered group of cells that covers plants' leaves, flowers, roots and stems. It forms a boundary between the plant and the external environment. The epidermis serves several functions, it protects against water loss, regulates gas exchange, secretes metabolic compounds,...
resulting in a white or silvery reflection. It is sometimes called blister variegation.
Pilea
Pilea
Pilea with 600–715 species is the largest genus in the plant family Urticaceae and one of the larger genera in the Urticales and eudicot rosids....
(aluminum plant) is an example of a house plant that shows this effect. Leaves of most Cyclamen
Cyclamen
Cyclamen is a genus of 23 species of perennials growing from tubers, valued for their flowers with upswept petals and variably patterned leaves...
species show such patterned variegation, varying between plants, but consistent within each plant.
Another type of reflective variegation is caused by hairs on parts of the leaf, which may be coloured differently from the leaf. This is found in various Begonia
Begonia
Begonia is a genus in the flowering plant family Begoniaceae and is a perennial. The only other members of the family Begoniaceae are Hillebrandia, a genus with a single species in the Hawaiian Islands, and the genus Symbegonia which more recently was included in Begonia...
species and garden hybrids.
Sometimes venal variegation occurs – the veins of the leaf are picked out in white or yellow. This is due to lack of green tissue above the veins. It can be seen in some aroids.
The blessed milk thistle, Silybum marianum, is a plant in which another type of venal variegation occurs, but in this case it is due to a blister variegation occurring along the veins.
Pigmentary
A common cause of variegation is the masking of green pigmentPigment
A pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which a material emits light.Many materials selectively absorb...
by other pigments, such as anthocyanin
Anthocyanin
Anthocyanins are water-soluble vacuolar pigments that may appear red, purple, or blue according to pH...
s. This often extends to the whole leaf, causing it to be reddish or purplish. On some plants however, consistent zonal markings occur; such as on some clover
Clover
Clover , or trefoil, is a genus of about 300 species of plants in the leguminous pea family Fabaceae. The genus has a cosmopolitan distribution; the highest diversity is found in the temperate Northern Hemisphere, but many species also occur in South America and Africa, including at high altitudes...
s, bromeliads
Bromeliaceae
Bromeliaceae is a family of monocot flowering plants of around 3,170 species native mainly to the tropical Americas, with a few species found in the American subtropics and one in tropical west Africa, Pitcairnia feliciana...
, certain Pelargonium
Pelargonium
Pelargonium is a genus of flowering plants which includes about 200 species of perennials, succulents, and shrubs, commonly known as scented geraniums or storksbills. Confusingly, Geranium is the correct botanical name of a separate genus of related plants often called Cranesbills. Both Geranium...
and Oxalis
Oxalis
Oxalis is by far the largest genus in the wood-sorrel family Oxalidaceae: of the approximately 900 known species in the Oxalidaceae, 800 belong here...
species. On others, such as the commonly grown forms of Coleus
Coleus
Solenostemon is a genus of perennial plants, native to tropical Africa, Asia, Australia, the East Indies, the Malay Archipelago, and the Philippines...
, the variegation can vary widely within a population.
Pathological
VirusVirus
A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...
infections may cause patterning to appear on the leaf surface. The patterning is often characteristic of the infection. Examples are the mosaic viruses, which produce a mosaic-type effect on the leaf surface or the citrus variegation virus
Citrus variegation virus
Citrus variegation virus , a member of subgroup 2 of Ilarviruses in the family Bromoviridae, is the causal agent of infectious variegation, a disease occurring all over the world, causing problems for production especially in some susceptible varieties of lemon and mandarin.Citrus trees infected...
(CVV). Hosta Virus X (HVX)Hosta Library: HVX has caused such dramatic and attractive mosaic-type variegations that, when the disease was new to the United States, affected plants were mistakenly thought to be new mutations and were registered as new cultivars.HVX-Infected Cultivars in the Marketplace
While these diseases are usually serious enough that the gardener would not grow affected plants, there are a few affected plants that can survive indefinitely, and are attactive enough to be grown for ornament; e.g. some variegated Abutilon
Abutilon
Abutilon is a large genus of approximately 150 species of broadleaf evergreens in the mallow family, Malvaceae. The genus includes annuals, perennials, shrubs, and small trees from 1–10 m tall, and is found in the tropical and subtropical regions of all continents. The leaves are alternate,...
varieties.
Nutrient
Nutrient
A nutrient is a chemical that an organism needs to live and grow or a substance used in an organism's metabolism which must be taken in from its environment. They are used to build and repair tissues, regulate body processes and are converted to and used as energy...
deficiency symptoms may cause a temporary or variable yellowing in specific zones on the leaf. Iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
and magnesium
Magnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...
deficiencies are common causes of this.
Garden plants
Variegated plants have been long-valued by gardeners, as the usually lighter-coloured variegation can 'lift' what would otherwise be blocks of solid green foliage. Many gardening societies have specialist variegated plants groups, such as the Hardy Plant SocietyHardy Plant Society
The Hardy Plant Society is a British charity that promotes the cultivation of hardy herbaceous plants. The Society was founded in 1957 by a group of gardeners and nurserymen. It has approximately 10,000 members and provides information about familiar and less well known perennials, how to grow...
's Variegated Plant Special Interest Group in the UK. Several gardening books which deal exclusively with variegated plants are available.
General references
- Variegated Plants - article from Union County College, New Jersey.
- BBC: Earth News - article suggesting that some variegation is to feign disease.