Variegation

Variegation is the appearance of differently coloured zones in the leaves, and sometimes the stems, of plants. Variegated leaves occur rarely in nature. Species with variegated individuals are sometimes found in the understory of tropical rainforests, and this habitat is the source of a number of variegated house plants.

The term is also sometimes used to refer to colour zonation in flowers, minerals, and the skin, fur, feathers or scales of animals.

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.

Some variegation is due to visual effects caused by 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.

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Wikipedia