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[[Image:VariegatedHollyBush.jpg|right|thumb|250px|Variegation in [[holly]] leaves]]
'''Variegation''' is the appearance of differently coloured zones in the [[leaf| leaves]], and sometimes the [[Plant stem|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.
==Chimeral==
Plants bearing such variegation are [[Chimera (plant)|chimeras]], 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 [[Cutting (plant)|cutting]]s, 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]].
==Reflective==
[[Image:PileaCadierei.jpg|thumb|right|Reflective variegation in ''[[Pilea cadierei]]''.]]
Some variegation is due to visual effects due to [[Reflection (physics)|reflection]] of light from the leaf surface. This can happen when an air layer is located just under the [[Epidermis (botany)|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. ''[[Cyclamen hederifolium]]'' leaves 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 [[Silybum marianum|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==
[[Image:TrifoliumPratense2.jpg|thumb|right|Leaves of [[Red Clover]] (''Trifolium pratense'') have a typical v-shaped variegation.]]
A common cause of variegation is the masking of green [[pigment]] 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, [[Bromeliaceae|bromeliads]], certain ''[[Pelargonium]]'' and ''[[Oxalis]]'' species. On others, such as the commonly grown forms of [[Coleus]], the variegation can vary widely within a population.
==Pathological==
[[Virus]] 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). 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.
==Garden plants==
[[Image:Variegated foliage.JPG|thumb|right|Variegated foliage used in an English garden. Plants shown include ''Aralia elata'' 'Aureovariegata' and ''Carex ornithopoda'' 'Variegata']]
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 Society]]'s Variegated Plant Special Interest Group in the UK. Several gardening books which deal exclusively with variegated plants are available.
[[image:Cryptocarya williwilliana - juvenile variegated.jpg|thumb|left|350px|The rare rainforest plant, [[Small Leaved Laurel]] showing leaf venation and [[variegated]] leaves]]
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Variegation. This term is usually applied to a class of variations, especially in leaf-coloration, in which the leaves become striped, banded, spotted, and blotched with yellow; white, red, and various other colors in connection with the normal green of other portions of the leaves. In the case of yellow-and-white variegation, the term albinism is sometimes used, especially when the plants are largely marked with white or yellow, as in Abutilon Sellovianum, Pelargonium zonale, and variegated forms of Evonymus japonica, Hydrangea hortensis, Hedera helix, Polyscias Guilfoylei var. Victoriae, and others.
Variegation. This term is usually applied to a class of variations, especially in leaf-coloration, in which the leaves become striped, banded, spotted, and blotched with yellow; white, red, and various other colors in connection with the normal green of other portions of the leaves. In the case of yellow-and-white variegation, the term albinism is sometimes used, especially when the plants are largely marked with white or yellow, as in Abutilon Sellovianum, Pelargonium zonale, and variegated forms of Evonymus japonica, Hydrangea hortensis, Hedera helix, Polyscias Guilfoylei var. Victoriae, and others.