It is not science fiction. It involves neither ninjas nor turtles. Cultivars really are mutant plants that can only be propagated by cloning. The word ‘cultivar’ is a portmanteau (two words combined into a single word) of ‘cultivated’ and ‘variety’. Unlike other varieties of plants that can be perpetuated by seed, cultivars must be cultivated by unnatural techniques to maintain their genetic distinction.
For example, ‘Alamo Fire’ is a variety of Texas bluebonnets with maroon flowers. The original seed were collected from a few naturally occurring variants with maroon flowers, and grown into more plants with maroon flowers, which provided more seed. No seed was collected from those that bloomed blue. By repeating this process of selection a few times, the variety was developed.
The variety ‘Alamo Fire’ is now sufficiently genetically stable to perpetuate itself, which means that subsequent generations will also bloom with maroon flowers. However, a few blue flowers might bloom in any generation; and unless they are weeded out before producing seed, they will eventually dominate until the entire colony reverts from maroon back to the more genetically stable blue.
‘Meyer’ lemon is an example of a cultivar. It must be propagated vegetatively by cuttings, or perhaps grafted onto understock. In other words, it must be cloned. It is a genetically unstable hybrid of a lemon and an orange, so plants grown from their seed would be very different from the parent. Many hybrids are so genetically unstable that they are sterile, and unable to produce viable seed.
Many variegated or dwarf cultivars of all sorts of plants are not hybrids, but are mutants. It is common for some arborvitaes to produce ‘sports’, which are simply mutant growth that is somehow different from the original growth. If a sport has a desirable characteristic, such as densely compact growth, variegation, or golden foliage, it can be cloned as a cultivar. Just like ‘Meyer’ lemon, a dwarf golden arborvitae is very unlikely to produce genetically similar seedlings.
Tony Tomeo 
This is a helpful post. For one thing, as obvious as it is, I’d never recognized “cultivar” as a portmanteau. For another, I’d wondered how the good people at Texas A&M had developed Alamo Fire. I’ve seen it, and it’s gorgeous, if a little odd.
As an aside, though related: I’ve always enjoyed finding white versions of usually colored flowers, like our basket-flower, Sabatia campestris), and bluebell (or prairie gentian). I’ve never found a yellow flower turned white — only the pink, blue, and lavender. Usually the white show up as individual flowers, but the bluebells will sometimes get a foothold and begin developing a colony. I presume it’s because there are enough of them that white is pollinating white.
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What an interesting observation. Steve Schwartzman made the observation that white variants are common among blue flowers. I did not notice that they are rare with yellow flowers. I would guess that blue is not that important for attracting pollinators, which might be why blue flowers are less common than flowers of other colors. Blue in flowers might be comparable to the autumn color of foliage, which happens, and even has the potential to be spectacular, but really serves no purpose. I know that insects and other pollinators can see infrared and ultraviolet that we can not see, but perhaps some pollinators either do not see blue, or do not find it to be attractive.
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I have future post coming up and you may have answered my question.
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What question is that?
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I will probably post it next week, but I have small ageratum I planted last year and now a nearly 2 feet tall one popped up. I think your post answered my question of where the large plant came from.
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Wow, that is some mutant!
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Finally I can understand how and why cultivars and hybrids develop and undevelop . Thanks
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Well, this is a simple explanation. There is more to it than that. Some hybrids develop naturally. Various specie of yucca hybridize freely with each other. The only reason they do not do so more commonly is that some are isolated from each other in the wild. Some oaks do the same, but the hybrids are sterile, so can not perpetuate a new specie.
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This is a good explanation of a confusing subject. I learned all this in classes but still need the refresher! 😊
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Thank you. I could have gone into more detail, but it is my weekly gardening column, for which, space is limited.
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The difference between those variations that seem more “stable” is that they are caused by dominant genes, whereas other variations are recessive. Dominant traits will “hide” the recessive in a generation, but if you get the right parent combination, the recessive will come out again. It’s like how blue eyes can sometimes pop up in a family of people with brown eyes. Also, any plant that produces seeds is usually the result of combined traits from different parents, just like in humans. That’s why clones are needed, because the next generation will also be a combination and not identical to the parents, again just like in humans. For me as a Biology teacher, genetics is the most fun subject to teach!
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