Yes, because the patent on that specific cultivar has expired and it is now part of the public domain. If a new patent has been issued, there must be enough of a distinction from the original plant to be warranted and it must be renamed and/or trademarked as well. Obviously, you cannot sell for profit propagations of the old selection under the new name - it's not the same plant, aside from being illegal.

Here is a link that might be useful: plant patents

Sometimes you cannot sell it under the old name either, because some NAMES are trademarked. You can, however, sell them legally under the proper botanical name.

You can always sell it under the registered cultivar name, which will be different from the trademarked name and attaches specifically to the plant. Trademarks are independent in that they are names only and will remain proprietary unless the trademark is not renewed. For example, Hydrangea arborescens 'Dardom' (registered cultivar name) is currently trademarked as White Dome (no single quotes around trademarked names). Down the road when the existing patent expires, one can freely propagate and sell the plant under the cultivar name of 'Dardom' or apply for an entirely new trademarked name of Snow Dome or White Hills or whatever or, if the trademark has not been renewed, under the original name of White Dome. All the trademark does is provide YOU (the grower and trademark holder) with the restricted use of that name. You can and do see the same plant being sold under different trademarks.

That's true, I should have thought to say that. This goes along the same lines as another thread about the pulling of plants from some marketing entities. Those very same plants may appear on the market under their registered cultivar name from different sources and not even be identified as such by most consumers. I was poking through one of the major breeders commercial grower websites last week and was pleased to see them list the registered cultivar names as well as those under which they were selling the plant.

I am not a professional gardeners, but I am getting into hybridizing and this question come to my mind:

If I bought a named cultivar or a patented plant and use it as parent or grandparent, and from that I get a plant that looks different (most likely color as that is my interest), and if I want to sell my new plants, do I have to pay the patent owner of the parent/grandparent?

If you are selling a "new" plant that has a patented plant in its parentage, no you do not need to pay royalties to the patentholder after the initial purchase. But you should be aware that you cannot asexually propagate the patented plant for your hybridizing program and that seed and many times pollen from many of these (usually hybrids) may be sterile.

Gardengal48, thanks!

You are not usually free to use sports or mutations of patented plants (asexually propagated) even though they may be different genetically from the parent plant. My growing licenses often spell it out to me that if any of the material sports, I must contact the patent holder and they own the rights to the mutated material.

What if I have mutation on some not patented plant that looks similar to a currently patented one?

Example. Mutation appeared on Euonymus fortunei 'Emerald and Gold' and it looks like patented Euonymus fortunei 'Waldbowli' (sold under the trademarked name Goldy). I have to do some observation and comparison, because the branch appeared this spring and is currently pinned to the ground for rooting, so I need to see whether it is stable or not. In a future I'd like to sell it. In case of complete similarity would it be reasonable and legal to assign new name without patenting? It's been produced on my property and I have photo and video proofs of this mutation.