To Revert or Not to Revert

Transcription

1 The attractive golden variegated foliage of this Pinto holly shows clear signs of reversion. Variegation can appear on any plant part bark, shoots, flowers and even roots. Variegated foliage, however, certainly has the strongest visual impact. Whether marked with stripes, streaks, edges, bands, spots or dots, I find variegated plants truly appealing. They come in a plethora of colors such as silver, white, cream, orange, pink, red and all imaginable shades of yellow, including gold. Nowadays practically every ornamental plant, from trees and shrubs to groundcovers, grasses, annuals, bulbs and perennials, comes in a variegated variety. Like many other things in life, variegated foliage should be used in moderation. Combining too much of it can create a chaotic landscape. Moreover, combining different variegated forms or using non-compatible color combinations is simply visually displeasing. Unfortunately, patterns mimicking variegation occasionally have a pathological character. Various viral infections produce mosaic patterns or streaking on leaves. Additionally, some nutrient deficiencies, such as iron or magnesium, can cause patterning to appear on foliage. Finally, insect infestation, lack of water or sunlight, or high temperatures may result in yellowing leaves. 1/6

2 The two types of true variegation can be easily distinguished. The most common is pigment variegation, in which cell mutations in one or more layers of the leaf cause the foliage to become patterned. This variation is found within the plant cells, called plastids. Plastids contain different colored pigments that determine leaf color. When a mutation occurs, the normal ratio of plastids is rearranged, some colors become more abundant, and the leaf takes on a variegated look. Most pigment-variegated plants are selected from naturally occurring mutations (sports) of the non-variegated (solid green) species. They may occur as seedlings or from branch sports (mutated branches on otherwise green plants). The patterned part is then taken from the mother plant as a cutting and propagated vegetatively to retain the trait. Structural variegation produces the attractive silvery color of this cyclamen foliage. The other type of true variegation is called structural variegation. Instead of affecting plastids, structural variegation exploits a phenomenon known as total internal reflection. Light is reflected from the upper surface of the leaf, resulting in a characteristic silvery variegation. Some well-known structurally variegated representatives include the begonia (Begonia spp.) and lungwort (Pulmonaria spp.), as well as house plants such as florist s cyclamen (Cyclamen persicum) and the aluminum plant (Pilea cadierei). 2/6

3 Some mutations are unstable and can revert to their original state. As a result, the patterned foliage of the plant becomes solid green. Reversion occurs in plants with pigment variegation only, as the foliage affected by structural variegation is virtually reversion free. Change doesn t happen overnight; reversion is a process that usually takes a few years. The reverted, solid green parts of the plant are usually larger, more vigorous and, as a consequence, grow faster than their bi-colored neighbors. The first signs of reversion can be easily missed or ignored. In such a case, a new, tiny shoot or branchlet seems innocent enough until it begins taking over an entire plant. Reasons for reversions are still not well known. It may be due to lighting, fluctuations in temperature, seasonality or other factors. Sometimes it s simply another mutation within the leaf s cells that causes the change from patterned foliage to solid green foliage. Variegation is the result of absent or masked green pigment (chlorophyll), which causes a reduction in photosynthesis. Consequently, variegated plants are less vigorous than pure green specimens. Therefore, the tendency for reversion can be perceived as a survival strategy that allows the plant to return to a more successful form. The Norway maple has a particularly strong reverting tendency. 3/6

4 It s not possible to reverse loss of variegation, but the reversion process can be retarded. There are two options. The easier one is to accept the new, emerging look of our plant. Because green leaves are more efficient than variegated ones at converting solar energy, they are stronger and more vigorous and will eventually take over. Consequently, there is nothing to do except wait patiently, and when reversion is completed, embrace the healthy, solid green plant. The majority of us, however, would most likely be disappointed, frustrated and even outraged by the fact that our plant has morphed into something else. Moreover, the emerging product probably wouldn t be as visually appealing as the original. The only solution is radical removal of every reverted part of the plant. In the case of trees or shrubs, solid green parts should be pruned out completely or cut back to the variegated leaves. The procedure is more complicated with herbaceous plants. The whole specimen should be dug up, the reverted part separated from the crown by cutting it out, and the plant re-planted. The sooner this is done, the better. This procedure usually slows the production of green leaf cells but doesn t stop it completely A white variegated wintercreeper sending green shoots. Notice that the plain green leaves are much larger than the variegated ones. 4/6

5 No pigment-variegated plant is immune to reversion, although some seem to be more prone than others. The Norway maple (Acer platanoides), particularly the cultivars Variegatum and Drummondii, and all variegated forms of wintercreeper (Euonymus fortunei) are good examples of repetitive reversion offenders. Some notorious reversion-prone houseplants include weeping fig (Ficus benjamina) and spiderwort (Tradescantia fluminensis). Albino growth produced by the silver-variegated English holly. Variegation is an oddity in the plant kingdom. There are few plants that are naturally variegated, in which case the variegation trait is passed on to offspring via genetic material in the seed. One example is the kiwi vine (Actinidia spp.). Some variegated plants, such as hollies (Ilex spp.), can occasionally produce bizarre cream or white shoots referred to as albino growth. (This is the opposite of the reversion process.) Albino foliage, although attractive, cannot gather solar energy and will eventually die back. Beautifully leaved plants have been and still are sought by plant enthusiasts, collectors and us, common gardeners. Our interest in the unusual assures survival of these odd beauties. Because they are truly special, inspecting them for symptoms of reversion and the occasional removal of green growth doesn t seem like such a high price to pay. 5/6

6 Text and photos by Gina Dobrodzicka Gina Dobrodzicka is a freelance writer and trained horticulturalist who volunteered with Master Gardeners of Ottawa-Carleton for five years. Currently, she volunteers with the Vancouver Master Gardeners Chapter, the South Surrey Garden Club and Darts Hill Garden Society. Her website is 6/6