Just about everyone is familiar with geraniums (really pelargoniams) grown primarily for flowers. Single or double, one-color or centered with white, they may be any shade of red, white, pink salmon or lavender. Some have scented leaves – rose, peppermint, lemon, and strawberry, among others. My favorites are the colored-leaf varieties.

Colored leaves occur when a mutation prevents part or all of a leaf from producing chlorophyll, the pigment that allows a plant to use the energy of sunlight to transform water and carbon dioxide into carbohydrates, releasing oxygen as a toxic by-product.

A mutation normally takes place in a single cell. If that cell is dividing, the daughter cells will have the same mutation. In the case of a geranium (or any genetically variegated plant) the critical tissue is what is called the meristem, found at the growing tips of the plant. Meristem cells are to a plant what stem cells are to an animal. If a mutation takes place in the meristematic tissue of a plant, and the mutation is such that chlorophyll production is inhibited in part of the leaf, the whole part of the plant that grows from that apex will show the same patterning. Where chlorophyll is absent, the plant will show whatever other pigments are present—usually carotenoids (red to yellow) and anthocyanins (red to blue.)

P. S, in my original post I missed some geranium colors.

Shoots that have less chlorophyll are less vigorous, but as long as they have some chlorophyll, they can be rooted to produce healthy plants. Back mutations do occur, and a colored-leaf plant will suddenly start growing a green branch. These green branches must be removed, as they are naturally the most vigorous and will take over if given a chance.

One thing I have found with several colored-leaf geraniums is that if light levels are low, as is the case during Alaskan winters, the variegation tends to disappear. When the light returns, so does the variegation. Unless, of course, a cell in a growth tip has mutated back to the green form. Then, as variegation returns to most of the plant, a few branches continue to have new green growth.

This happened to the plant in the photograph. It’s now had the two major green branches removed, and I hope new growth from the remaining branches with their white-centered leaves will remain variegated.

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