OF THE WEEK
Dr. T. Ombrello - UCC Biology Department
Look around the cultivated landscape and note the number of variegated (with leaves of multiple colors) plants we grow. Compare this to natural situations and it readily becomes apparent how well represented variegation is in the landscape. Some horticulturists consider variegation to be unnatural and gaudy, and in a few cases this surely is true. But, gardeners in general have had a love for variegation that goes back hundreds of years.
Variegation in plants can occur for a number of reasons, but most commonly it is a genetic “experiment” or “mistake” (depending on one’s evolutionary point of view) that occasionally appears in nature. A white variegation is the result of a plant’s inability to produce any pigment in that area. Orange, yellow, and light green leaf colors result from a lesser production of the green pigment chlorophyll, unmasking the orange carotenoid and yellow xanthophyll pigments and allowing them to appear. Shades of pink, red, and purple are the result of anthocyanin pigments. If produced in sufficient quantities, they can mask even the green chlorophyll. Interestingly enough, most temperate deciduous trees and shrubs produce these colors by these same mechanisms in the Fall, but variegation only applies to leaves with these colors all the time.
|A close-up of a variegated Rubber Plant (Ficus elastica) growing in one of Union County College's greenhouses.|
|A close-up of a Ficus benjamina 'Golden Princess' growing in one of Union County College's greenhouses.|
A variegated pothos (Epipremnum aureum 'Marble Queen') growing in one of Union County College's greenhouses.
There are also plants with silver colors on their leaves, but there are no silver plant pigments. The “silver” of the indoor Panda Plant is the result of light reflecting from the numerous unpigmented hairs that cover the leaf and give it a furry appearance. The appropriately named Aluminum Plant has patches of silver on its leaves because the unpigmented upper layer of the leaf (the epidermis) is lifted from the layer below. Some Colorado Spruce trees appear silver/blue because their needles produce a wax that masks the green color beneath.
Variegation can occasionally be the result of a virus infection, producing mosaic or streaked symptoms on leaves and/or petals. “Tulipomania”, a horticultural craze for tulips with streaked petals, rampant in 17th century Holland, was based on virus infected plants. The variegated ornamental Flowering Maple (Abutilon pictum ‘Thompsonii’ ) is in much more demand than its non-virus infected counterparts.
The pattern of variegation on a leaf depends on which cells carry the genetic information for the non-green color. Sometimes it is totally random and gives a speckled appearance, or can be quite uniform. For example, Dracaena marginata, a common indoor plant, has green leaves with red margins. Not all of the cell layers of the leaf extend to the edge, and in this case the layers with abundant red pigment do, but the layers with only green pigment do not.
Some variegations can be unstable, with variegated plants producing all green or all white (albino) shoots or leaves. Wandering Jew plants, Swedish Ivies, English Ivies, Screw Pines, Creeping Figs, Peperomias, and Geraniums are just some of the common species whose variegated members this writer has seen revert. This can occur in spite of efforts to remove all green or albino shoots as they appear. Some things are just not meant to be.
Propagating variegated plants can also bring about some surprises. While most cuttings of variegated plants produce identical offspring, leaf cuttings of yellow-banded snakeplants will yield all green offspring. Seeds from variegated plants can “breed true” with variegated offspring, but they are just as likely to produce all green or albino seedlings. The latter are doomed since albinos cannot photosynthesize to make food. All this adds an interesting dimension to plant propagation.
Variegated plants often have more exacting environmental needs than the all green members of the species. They often cannot tolerate very low light conditions (less chlorophyll for photosynthesis) but, on the other hand, may scorch under bright light (less protective pigmentation). Less vigor, smaller leaves, and increased sensitivity to temperature extremes are other features associated with variegation. These characteristics may explain why there are not that many variegated plants found in nature. Unless variegation has some adaptive feature, such as attracting pollinators or repelling herbivores, it is a liability that makes variegated plants less likely to successfully compete with all green plants. The “struggle for existence” in nature eliminates the less adapted.
We as a species, however, protect and perpetuate these oddities of nature. Our interest in the unusual assures their survival under our care.