Mutants are the source of many of our favorite cultivars of otherwise simpler specie. Many cultivars of plants with compact, pendulous or fastigiate (strictly vertical) growth, or variegated, bronzed, golden or otherwise abnormally colored foliage, were derived from ‘sports’, which are mutant stems that appear on otherwise normal plants. Thornless blackberries were sports of thorny cultivars. Fruitless mulberry is a sport of white mulberry. There is no shortage of mutants.

https://tonytomeo.wordpress.com/2018/05/07/cultivars-are-the-real-cloned-mutants/

https://tonytomeo.wordpress.com/2018/05/06/sport/

By nature, mutants are genetically unstable. A few can easily mutate back to their original and more genetically stable characteristics. Variegated plants are notorious for developing simple green unvariegated foliage. Because it has more chlorophyll, the unvariegated foliage grows faster, and has the potential to eventually overwhelm and replace the variegated foliage. That is why green sports should get pruned out of variegated plants.

‘President Roosevelt’ is the most popular of the few variegated rhododendrons. In nursery production, it gets pruned somewhat regularly to remove green sports. Variegated specimens are rare in landscapes because almost all revert to unvariegated foliage within only a few years.

‘Yellow Wave’ is a cultivar of New Zealand flax with pendulous yellow striped foliage. It can be seen in front of the upright greener foliage in the background. These are not two separate plants stuck together. The more vigorous green foliage is a reverting sport that should have been removed by the ‘gardener’ who is supposed to be ‘maintaining’ this landscape. The green sport is now so developed that it can not be removed without damaging the rest of the ‘Yellow Wave’ growth. It will undoubtedly be left to overwhelm and replace it. Fortunately, the upright green foliage is about as appealing as the ‘Yellow Wave’, so no one will notice the inadequacy of the maintenance. No one ever does.