Regarding species and natural variation, the most important consideration has to be that plant naming/classification (or naming/classification of any organism, for that matter) is a human activity and not something that is set in stone by nature. Reclassification happens when scientists decide that certain plants belong in the same species or genus or belong in different ones. Taxonomists (those whose specialty is classifying plants) are not always of the same mind on this, and sometimes differ widely. When I was in college botany, I was introduced to 'lumpers' and 'splitters', names describing scientists who put lots of plants together in the same species or genus, and those who prefer to separate plants out on even the most seemingly insignificant characteristics, respectively.
Once I got the "lay of the land" about taxonomy, I became a lot less religious or legalistic about plant naming or classification. To me, you need more than a scientist's argument about what a plant is; you need actual growing experience, genetic work (as in actual breeding), and long-term observation with data recording. Simply finding a "new" plant and tacking a new name onto it is not enough, IMHO. It is enough for a new published article, though, which is what scientists are often forced into because of the "publish or perish" pressure they are under in academia.
And then there is the ultimate dillemma in biology, which is what is known as the "species problem". In lay terms, it means that scientists are not at all in agreement on what a "species" actually is. One would think that this would be easy to figure out, but it is not, and as in taxonomy, there is a really wide range of opinions on the nature of a species. Darwin's "On The Origin of Species" did NOT solve the problem -actually it did not actually address it!
So we do need names for plants that we all can agree on, but it doesn't pay to get too worked up over it. Until we get a truly concrete method of determining a true species, debate will rage on.
OK, that's my $0.02 US!!!
