[AndrewC]

And if British botanists tell me that this plant is something never before seen, and most likely a brand-new species, what choice do I have but to accept that, too?

Though some may have a problem with the presence of a new "species", for others it is the relevance of the new "species" to the question of a Darwinian type evolution. Part of the problem stems from the lack of a clear and consistent definition of "species".

For example in the bone department

       Researchers debated where in humankind’s family tree the new fossil belonged, eventually describing it as a new species called Homo rudolfensis. They drew a question mark in diagrams of human evolution, wondering how these two groups of humans interacted and which one gave rise to the peoples of today.
       Enter OH 65: Its upper jaw and teeth provide what Blumenschine called “a key anatomical link” between the lower jaw of H. habilis and the toothless H. rudolfensis cranium.
       In their new paper in Friday’s issue of Science, Blumenschine and 16 co-authors conclude that all of the specimens are similar enough to be called H. habilis, and H. rudolfensis is not a separate species at all. At the same time, they suggest that several smaller-brained specimens do not belong in H. habilis.

[general_re]

That's a bit different - in those cases, we have little choice but to infer from anatomical evidence whether or not those specimens represent different species. For paleontology of any stripe, we have a limited amount of noisy data, and we can only do the best we can with what we have. But here, we have a bit more direct observation - this plant is demonstrably incapable of viably interbreeding with any other variety of plant, including its own parent species, which fits virtually any definition of "species" that we might reasonably consider.