Why are Parts of my Plant Changing Colour?
Variegation is when the foliage of a plant exhibits two or more colours of foliage. Most often this is where there are pale areas on green leaves. But it can be streaks of red or purple, blotches of pale green and other variations on this theme.
There are several possible reasons for variegated foliage:
- A genetic mutation within the growing plant may stop or reduce the production of chlorophyll* in some of the tissues. Those parts of the plant that originate from tissues that have the mutation will be pale or they may look red if the red pigment in the plant is now visible without the chlorophyll to mask it. Such variegation can usually only be passed on by vegetative reproduction using cuttings that have both the wild type and the mutated tissue. Seeds are likely to be either wild type** or mutated. If the seeds are mutated, they will be fully pale and are likely to be non-viable because they will not have chlorophyll to photosynthesise.
- Akin to the genetic mutation, discussed above, is viral variegation. An infection with a virus can cause a genetic mutation or interfere with the genetics of chlorophyll production. The results will be like that above.
- Some variegation is not caused by a (recent) mutation. Plants with patterned variegation such as Calathea spp. and Ctenanthe spp. may have evolved their patterns to confuse insects that might eat the leaves, but plant breeders will have selected out the most attractive patterns and this artificial selection has produced a variety of striking patterns and colours. Such variegation can be passed on in seeds.
- Another cause of variegation is a blister or reflective variegation. This is where small pockets of air form in the leaves above the pigmented layer. The blisters reflect light giving a silvered appearance. The variegation of Peperomia argyreia is one such example.
Many plants are selected and bred for their variegation. They are deemed to be attractive and although the loss of pigmentation may make them less fit for survival in the wild, in the ‘captivity’ of our homes and gardens, we ensure their fitness to survive. However, on occasions the variegation can be lost, fully or partly, for various reasons:
- If a new branch or bud forms from tissue not containing any of the variegation causing genetic mutation, the leaves will form as the wild type and without variegation. This is common in variegated hedging plants.
- A similar thing can happen if the variegation is caused by a virus and the new limb is virus-free.
- Wild type genetic variegation is more stable and unlikely to be lost, but it could happen if seeds are produced through hybridisation with non-variegated forms or, very rarely, by a reverse of the original mutation.
- Loss of blistered or reflective variegation is also rare, as it requires either a mutation or some fault in plant development that stops the blister structures forming.
- Also, under stress, the physiology of the plant may be pushed to increase the production of chlorophyll to compensate for low light, and this can cause the variation in colour to be lost. This effect may reverse when stress is removed.
If you have a variegated plant (houseplant, tree, shrub or other) which is losing the variegation you want to keep, you should immediately prune out any stems or branches that have lost the variegation.
If the variegated plant is stressed by lack of nutrients such as nitrogen or iron it may lose the green colouration in wild type areas. So the contrast between these and the mutated low pigment areas will be lost. You can ensure the contrast of variegation of your plants is maintained and enhanced by feeding your houseplants with Gro-Sure Houseplant Pump'n'Feed and Mist'n'Feed, and your hedges and other ornamentals with PLANThealth Buxus Feed.
*Or one of the other pigments in plants.
** Wild type is the phenotype (observable characteristics) of the typical form of a species as it occurs in nature.