You have an interesting study, but I think you need to take crbjork’s key into account before I can come to the same conclusions as you have as achene color doesn’t seem to be as important there. It’s pretty clear that most of the North American taxonomy dealing with introduced Taraxacum species doesn’t work well. The question is, does that support creating a finer, more European style system or lumping everything together. In my mind, this fact of bad flora treatments doesn’t support or diminish support for either, it simply informs what philosophy we want to take on the species concept. I tend to be on the splitting end of the spectrum and while I’m not sure how I feel about how fine the microspecies taxonomy is in Taraxacum, I am open to the idea.
Regarding your second post, I’m not particularly sympathetic to the argument from human taxonomy. Such an argument only leads to not recognizing subspecies or varieties at all. Such a taxonomy is inflexible and too imprecise for me to consider workable in many cases. Furthermore, I believe it would discourage the discovery of new species and the conservation of threatened populations. I can think of many examples where plants that were previously thought of as varieties turned out to be good species. What’s more, this argument doesn’t even apply well to the question of whether to recognize microspecies as humans are not apomictic.
Regarding the argument of public utility, I’m not particularly sympathetic to that argument in this particular context either. In the context of education, (e.g., teaching the best taxonomic categories to use and to not be dismayed by not getting to species level) I think there’s a lot to be discussed but taxonomy should ultimately reflect our best understanding of the world (and we can argue about what that is) regardless of how the public views it. To give some semblance of an analogy, high school students hating higher-level math and most students not ever using it in their lives is not a good argument for not articulating higher-level math (maybe an argument for not teaching it at certain levels, but certainly not an argument for not teaching it at any level).