There is an old French saying, vive le différence ("long live the difference!") We might also say, "variety is the spice of life." However we express it, it rings true that we adore things that "break the pattern", and when it comes to foliage plants, variegation (leaves with white, cream, gold, silver, or other shades added to the usual green of the forest) is a feature most plant lovers really go for! But what is variegation, really, where does it come from, and why does it sometimes seem elusive and transient?
Hoya kentiana variegata
First off, we need to understand that more than one mechanism can lead to variegation. In some cases, it's as simple as an environmental factor like reduced (or increased) light. In other situations, the cause is genetic. And variegation, both genetic and non-genetic, can be the result of virus activity, especially those retroviruses that carry bits of genetic material with them when they infect plants. In the mid-1630s, tulpenmanie (tulip fever) struck Holland, as collectors began to obsessively cultivate, trade, and hoard bulbs of the Tulip, a plant originally brought to Europe from Asia Minor through trade routes. A high point of the phenomenon occurred when virus infection created some amazing variegated blossoms on certain types of Tulips, some of which could be carried over from one generation to another.
In the case of variegated foliage, whatever the ultimate cause, variegation results from the absence of chlorophyll, the green pigment that traps sunlight in order to create energy for the plant.
Variegated Philodendron
In the 21st century, Aroids are the greatest focus of the variegation obsession, especially Monstera and Philodendron species, but also many others. Additionally, Hoyas, Begonias, Gingers, Goeppertias (formerly known as Calatheas), Draceneas, Agloanemas, and many other groups of popular houseplants include at least some highly sought-after variegated varieties. If I had to pick a "poster child" for the current variegation phenom, it would probably be the Monstera 'albo' (Monstera deliciosa albomarginata), with its white-on-green marbled and half-moon patterned leaves. Though tissue culture and offshore cultivation have helped greatly reduce the price, these plants still average between $150-$300 for a smaller, well-started specimen, and a full-grown specimen with nice variegation could easily range into the multi-thousand dollar category.
Monstera deliciosa albomarginata
In the case of most of the currently-popular variegated Aroids, their coloration is the result of spontaneous mutations, carefully cultivated and propagated by horticulturists who saw their potential. The challenge of producing variegated plants for market is quite different from reproducing many other traits. If a plant has a lot of variegation, the result is often decreased vigor, due to a large part of the plant's leaf surface area not being able to carry on photosynthesis. This can lead to longer times needed for propagation and lower overall success rates. Plants like the Monstera albo, Monstera 'Thai Constellation', and various trailing Philodendrons are most quickly reproduced by taking internodal cuttings (cuttings of the main growing stem that include one or more nodes, points where aerial roots are produced. Of course, suitable material for such cuttings is very limited on each parent plant, and it takes a long time to develop a large stock of specimens to provide cuttings. Tissue culture technique, in which a carefully selected bit of tissue is extracted using sterile technique and treated with appropriate plant growth hormones, then allowed to grow in an artificial culture medium in glass flasks in a laboratory. It takes time, but this method ensures production of many identical plants from a single piece of tissue taken from a desirable parent, and over time can help reduce the cost for bringing plants to market.
Philodendron 'Pink Princess'
For the home grower, variegation lends visual appeal, making a large and well-cared-for specimen a standout in any collection. In terms of care, variegated plants can vary considerably, depending on the genus and variety, but it's important to study their needs and treat them appropriately. Even in the case of genetic mutations causing variegated leaves, it turns out that environmental conditions can have a major impact on how the plant turns out. For instance, some variegated species need more-than-average light, while most prefer indirect light. Some need a particular soil pH, watering conditions, or other special considerations, and meeting these is necessary for the plant's genetic tendency to fully express itself.
Syngonium 'albo'