Variegation in holly leaves

The term is also sometimes used to refer to colour zonation in flowers and minerals.

Chimeral variegation

Plants bearing such variegation are 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 meristematic tissue losing the ability to produce chloroplasts, 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. 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. 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.

Variegation due to reflective effects

Reflective variegation in Pilea pumila.

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.

Variegation caused by other pigments

Leaves of Red Clover (Trifolium pratense) have a typical v-shaped variegation.

Pathological variegation

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.

Variegation in garden plants

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.

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