Varigates - November 2016, April 2015, January 2013, March 2012, October 2010, November 2008 & 2007
Variegation is the appearance of differently colored areas leaf or stem due to a partial loss of chlorophyll. This is usually due to genetic mutation, developmental abnormalities or certain viruses. People have also been able to induce variegation in plants through the use of radiation or treatment with certain chemicals. The scientific details of exactly how variegation arises in plants, and how it is maintained (or lost), are too complex to go into in depth here.
The pattern may be consistent and well organized (e.g. many Agave) or it may be randomly distributed (e.g. most variegated cacti). Plants with patchy or mosaic patterns of variegation are often the result of a cell mutation that is fairly random. In other words the plant may be prone to producing cells without chlorophyll sporadically, and when that cell appears it divides many times (just like normal cells). Some plants have fairly organized and consistent variegation patterns. That is quite often due to different meristem (i.e. mother) cells being responsible for forming different layers or parts of a leaf or stem. For example, if the meristem cells responsible for making the outer edges of a leaf have the variegation gene while meristem cells for the center of the leaf do not, you will get a consistent pattern of white edges and a green center.
Plants totally lacking in chlorophyll (achlorophyllus), such as the brightly colored grafted Gymnocalycium cultivars are technically not variegated, but are considered so for the purposes of cacti and succulent shows. Keep in mind, a plant is not variegated just because the leaves have colored areas. It must be partially lacking chlorophyll as well.
Variegated plants normally have white or yellow patches and streaks, but can also be colors including red, orange, brown, pink, and purple. Colors other than white are due to the presence of colored plant pigments such as anthocyanins and carotenoids.
Variegation is known throughout the plant kingdom, but is rarely seen in the wild. The reason variegated plants are common in horticulture is that people like the color and unusual nature of these plants. When a rare variegate appears in a batch of seedlings we are keen to grow it, propagate it and spread it around!
Variegated plants have a place in most gardens. The strange and colorful patterns bring unique visual interest to any collection. In cacti and succulent shows, variegates generally compete against other variegates to put them on an equal footing. The Intercity Show gives the following guideline for showing plants in the variegated category: "Plants with 30% or more variegation may only appear in such category except for variegation in Agave, Gasteria, Sansevieria."
In general, variegated plants grow slower and are smaller than non-variegates of the same species. They also tend to sunburn easily and most need more sun protection than a typical member of the species. Ironically, variegates also have less shade tolerance than their non-variegated counterparts. The reason for this is that chlorophyll "soaks up" the sunlight to make food. With less chlorophyll the plant needs more light to get the same amount of food, but at the same time the more delicate tissues are exposed to the light without any protection. A good rule of thumb is simply not to grow variegates in extremely bright or dark situations. Otherwise, the care of a variegated plant is the same as for the normal form of the species. A large well grown variegate of any species is truly an achievement.