Variegated plant problems are caused by a variety of factors. One of them is sunlight. Another one is light intensity. Light intensity causes the color change in plants. Some types of sun exposure cause green leaves while other types cause blue or purple leaves. There are many types of sun exposure. Sunlight comes from various sources such as direct sunlight, artificial light, and even the moon. The type of sun exposure affects the color change in plants. For example, if it is indirect sunlight then there will not be any effect on the color change in plants because they have no contact with the sun’s rays at all. However, if it is direct sunlight then the color change in plants will be affected.
The most common form of sun exposure is direct sunlight. Direct sunlight is when the sun shines directly on the plant’s leaves.
When this happens, the chlorophyll in the leaf cells absorbs some of the light energy and turns into sugars which are stored in specialized structures called photosynthetic pigments. The other colors of light, which are absorbed by chlorophyll, appear as color in the leaf. This is why we see green plants.
When some of the different wavelengths of light from the sun shine on a leaf, only some of the wavelengths are absorbed by the leaf. The rest go elsewhere such as the atmosphere or into other objects around the plant.
This is why leaves are green; they reflect green light and absorb all other wavelengths. This is why when you go out in the sun you should wear sunscreen or clothes to protect your skin because the sun’s rays are dangerous and can cause skin cancer.
However, chlorophyll is not the only pigment found in plant cells. Carotenoids and anthocyanins are also present.
These pigments absorb some of the wavelengths of light that chlorophyll doesn’t absorb. This is why some leaves are red or orange (anthocyanin), or yellow, orange or even brown (carotenoid). Carotenoids can also be present in the leaf veins of green leaves, which is why you see patterns like that of a leaf of pennywort. The bottom line is carotenoid and anthocyanin is only produced when exposed to intense light.
Other pigments also occur in the leaf in
addition to chlorophyll, carotenoids and anthocyanin. These are mainly present in the leaf veins.
Chlorophyll is present throughout the leaf, but there are other pigments that are only present in the leaf veins. These are present in all plants, but the color that they give is not always obvious. Sometimes they reflect light and obscure the color of the underlying vein. However, when an outer leaf is damaged or dies then these underlying vein colors are revealed as in the case of variegated plants.
There are also other pigments that are always present in different proportions in the leaves. These are not caused by light, but by genetics and other factors.
However, when the leaf is damaged the underlying veins become more prominent and you can see the other colors produced by these pigments. The colors that these pigments produce are yellow (xanthophylls), purple (anthraquinones) and sometimes red (catechines).
An example of this is in the leaves of most houseplants.
Leaves are not green on the inside; they are translucent and you can see through them. They just look green because the green wavelengths are reflected back to your eye.
A leaf looks green because only green light is reflected back to your eye
The colors that we see in leaves are usually from pigments that absorb some of the wavelengths of light in the spectrum while others are absorbed by chlorophyll. Most houseplants have green leaves, but if you look at the veins of these green leaves you will see that they are a silvery color.
If you break the leaf, then this silver color appears in the leaf blade as well. This is due to a combination of two factors. The first factor is genetics: some species of plants just have naturally green leaves and other species have naturally silver veins (even when they are not exposed to light). The second factor is light. This is why when you look at a leaf under a microscope you do not see the vivid colors that we normally see in a leaf. You just see a mass of green, but it is really a mixture of colors.
These other pigments are not normally seen because they are masked by the green of the chlorophyll. It takes damage to the leaf for these underlying colors to become visible and this may be due to insect damage, disease or physical damage caused by handling.
Green leaves that receive lots of light become yellow, while leaves that do not get light turn completely silver. This change in coloration is not related to age.
When a leaf is damaged, the green chlorophyll retreats from the damaged area and over time you are left with just the underlying colors produced by these other pigments. Silver veins become more visible when the green chlorophyll retreats from the damaged area.
Yellow becomes more prominent when there is a lot of light. These other colors produced by pigments in the leaf veins are not always obvious, but their colors can aid in plant identification. The other pigments are not as common in the leaves of plants and some of them such as the anthraquinones occur only in the leaves of a few species.
Anthocyanin is what gives blue flowers their color and red flowers such as hibiscus their color. Red only occurs in a few species of plants, but when it does occur the red becomes more visible.
Most plants will react to physical damage by retreating from the area that was damaged and producing other pigments, which mask the chlorophyll from view. This is one of the reasons why houseplants sometimes look sick.
They get a small cut, which results in a loss of chlorophyll from that area. While many plants contain these pigments, very few have blue leaves. The two examples in our database are Syngonium podophyllum (Angular Solomon’s seal) and Wisteria floribunda var. australis (Australian wisteria).
Purple leaves do not occur in nature, but can be created by man. They are created by mashing up purple carrots and mixing the mash into normal green plant food.
The purple food coloring in the plant food is not strong enough on its own to alter the color of the leaves. These purple leaves also have a very unusual smell.
Insects sometimes cause damage that leads to bleeding of the plant and the loss of chlorophyll. This damage is most often seen on houseplants, but it can occur in your yard as well.
There are two types of insects that cause this damage: aphids and caterpillars.
Aphids are small green insects that cluster on the leaves of plants and suck the sap. They do not destroy the plant, but they can cause it to become sickly looking and reduce the growth of the plant.
If you crush an aphid you will see a red liquid, which is not blood, but a sweet fluid called honeydew.
Caterpillars are the larvae of moths and butterflies. In both cases the insects weaken the leaf by sucking out fluids and they also introduce viruses into the plant.
Aphids are tiny green, brown, black, or even white insects that cluster on the leaves. They tend to congregate where the leaves join the stem.
You may see little specks of dried sap on these areas–this is the waste left over from the aphid’s feeding. They are seen on plants most often on leaves that are beginning to turn yellow. They are green like the aphids, but have a distinct stripe pattern down their back. If you crush a caterpillar you will see that it has a black blister on its abdomen. This is not a disease and does not affect humans or other animals if you eat the caterpillar.
Caterpillar eggs usually look like small tiny green orbs that tend to be grouped on the undersides of leaves. The caterpillars themselves can range in color from green to brown or even black.
The mature caterpillars are very recognizable, having several lengthwise stripes and sometimes sporting a curious “horn” in the middle of the back. They too congregate on the undersides of leaves where they can best conceal themselves from predators.
It is very difficult to prevent these insects from attacking plants. Most pesticides are either too weak or too strong to safely use on houseplants, but some insecticide treatments on the market are safe for houseplants, and these can help control the problem.
For aphids it is best to wash them off the plant with a high pressure spray from your hose. Be sure to direct the spray under the leaves as well.
The most important thing to do is to act quickly before the insects spread to other plants. Many insecticides are only effective if used immediately after an insect infestation.
Many insects have a natural predator that will help control their numbers. These predators include ladybugs, who eat the aphids before laying their eggs; parasitic wasps, who lay their eggs inside caterpillars; and birds, who feed on caterpillars and aphids.
If you have a severe insect problem you might want to consider buying some of these predators to help control the infestation.
If the plant remains infected with viruses, no amount of chemicals or predators will help. The only solution is to discard the plant and buy a new one.
It is important to remember that MANY common plant pests are not really insects at all. These include mold, fungi, and other things you can’t readily see without a microscope.
Most of these are spread by an infected plant and can be carried to your plant on your clothing, on tools, or in the soil.
One of the most common plant diseases is caused by a fungus called “Pythium”. It enters the plant through the roots and travels throughout the entire system, stopping up the water transportation system of the plant.
This leads to leaves that are yellow and spotted, with a dark brown or black areas near the edges. The older leaves will begin to wilt and fall off, after which new leaves will also be infected.
Sources & references used in this article:
Pattern reversal in variegated plants; an explanation of reversal in coloration in the histogenic type of variegation. by H Dermen – Journal of Heredity, 1950 – cabdirect.org
Three graft-transmissible diseases and a variegation disorder of small fruit in New Zealand by GA Wood – New Zealand journal of crop and horticultural science, 1991 – Taylor & Francis
Growth Inhibition & Bleaching in Higher Plants & Euglena by O-Methylthreonine; Reversal by Isoleucine by RA Gray, D Hendlin – Plant physiology, 1962 – ncbi.nlm.nih.gov
Excision of an active CACTA-like transposable element from DFR2 causes variegated flowers in soybean [Glycine max (L.) Merr.] by M Xu, HK Brar, S Grosic, RG Palmer… – …, 2010 – Genetics Soc America
Purification and properties of a new virus from black currant, its affinities with nepoviruses, and its close association with black currant reversion disease by A Lemmetty, S Latvala, AT Jones, P Susi… – …, 1997 – Am Phytopath Society
The development of the leaves in certain periclinally variegated plants by K Massey – Journal of Genetics, 1928 – Springer
… disease incidence in a range of blackcurrant genotypes, differing in resistance to the blackcurrant gall mite (Cecidophyopsis ribis) and blackcurrant reversion disease by AT JONES, RM Brennan, WJ McGAVIN… – Annals of Applied …, 1998 – Wiley Online Library