Variegated foliage plants are attractive to gardeners because they offer a change from the plainness of solid colored leaves. Of course, flowers can be variegated, too, and often for the same reasons as foliage, but this article concentrates on variegated foliage and the different types of variegation.
Variegation might be defined as the presence of differently colored zones or areas in leaves and sometimes the stems of plants. Leaves may be edged or patterned in a different color, or they may have pale or light patches. Variegated foliage may exhibit different colors in irregular patches or streaks, or the different colors may be consistent from leaf to leaf. Some plants may produce a stem or branch that is variegated while the rest of the plant is green, or a variegated plant may revert to its solid green form.
TYPES OF VARIEGATION
A chimera is a plant or plant part made up of layers that are genetically different. Some of the layers are able to produce chlorophyll while other layers are not, resulting in a variegated plant with white or yellow colored zones on an otherwise green leaf. Three types of chimeras are recognized: mericlinal, periclinal, and sectorial. They are differentiated according to how many layers of plant tissue are involved, and where on the apex of the growing point a mutation occurs.
The vast majority of variegated plants are a result of chimeral variegation. This type of variegation may be randomly spread about the plant, or it may be consistent and symmetric in appearance throughout the whole plant. While variegation in some forms is relatively stable, in other forms it is unstable and may even revert to the green form. Because variegated plants cannot produce as much chlorophyll as their all green counterparts, they are less vigorous.
Some chimeral plants will come true-to-type from stem cuttings (periclinal), while others will not (sectorial or mericlinal). None of them come true-to-type from leaf or root cuttings or from seed. Hollies and ivies are examples of periclinal chimeral variegation.
Reflective or Blister Variegation
The aluminum plant (Pilea cadierei) and others with patches of silver on their leaves exhibit a type of variegation called “blister” or “reflective” variegation. In these instances, the unpigmented upper layer of the leaf (epidermis) is lifted from the pigmented layer below by a blister, which causes an air pocket to form. Light reflecting from the membranes of the transparent air pocket cause the area to appear silver. Blister variegation can be expressed in scattered places on a leaf, along the veins of a leaf, or between the veins. Since blisters are a part of a plant’s genetic makeup, plants with blister variegation come true from seed, cuttings, and other common means of propagation.
Pattern-Gene, Pigmented, or Natural Variegation
Some plants have genetic instructions for producing leaves with numerous pigment colors. Such natural variegations are permanent and will be reproduced in seed-grown progeny. The Maranta, for instance, will always make its characteristic red and green fish-bone pattern, and eyelash begonia (Begonia boweri) will automatically produce its characteristic eyelash edges. Seedlings from coleus will be similar to the parent, but more variations may be present due to selective breeding of the genus.
Some plants, such as Actinidia kolomikta (variegated kiwi vine), with its naturally white-tipped leaves due to pattern-gene variegation, demonstrate developmental variegation as they become progressively pinker as the season progresses.
Various viral infections are sometimes responsible for variegation in some plants. The mosaic viruses cause a partial breakdown of chlorophyll resulting in irregular patches of discoloration, usually white or yellow, on a leaf surface. Hosta Virus X has caused dramatic and sometimes desirable variegation in hostas and the citrus variegation virus (CVV) gives us variegated citrus plants. Variegated Abutilon varieties are a result of mosaic virus, and they can survive indefinitely and are more popular than the solid green types. Viral infections are not as common as other types of variegation. Viral infections significantly weaken some plants, but others are less affected.
Viral diseases may be either accidentally or purposely introduced. Most of us think of a disease as undesirable in plants. Usually, of course, we try to avoid anything that smacks of a disease in our treasured collections. While it is true that some viral diseases may cause excessive weakening and eventually death in certain plants, this is not true in every instance. The effects of some viruses are less severe and the affected plants can survive indefinitely and are attractive and desirable garden specimens.
Other causes of variegation in plants will be discussed in a future article. For now, it is enough to examine the different types of variegation. It may be comforting to some people to know that all variegated plants are not infected with a virus, as this is a common misconception. Many are perfectly healthy and vigorous, and their variegation comes about as a result of predetermined genetic instructions.
For plant identification and photograph credits, mouse over the pictures. Thanks to Dave's Garden photographers who are willing to share their work with DG writers. Uncredited photographs are the author's.