I have had the deepest scepticism about award winning books and their levels of research since encountering Joseph O'Connor's absymal "Star of the Sea" in which on board ship in 1847 the ship's doctor identifies a sample taken from a pustule on a passenger as syphilis at night, by the use of a microscope and then tells the patient that the syphilis organism "is a living thing, just like us. It does what it has to in order to survive."
Now, quite apart from my scepticism about the ambient light levels between decks on an 1847 steamship and the quality of microscopic enhancement (frankly, in those conditions I'm surprised anyone could have accurately identified anything smaller than a medium-sized capybara) you cannot in fact identify a spirochaete like that, which is why Wasserman had to come up with the Wasserman test for diagnoising syphilis. In 1909.
But quite apart from that, Snow wouldn't publish his epic paper on cholera transmission until 1849 which was the very beginning of the germ theory of disease, and it wasn't until Pasteur et al about twenty years later that the bacterial theory of infection was even properly developed, and people like Florence Nightingale went to their deaths claiming it was quackery.
Oh, and I forgot to mention the said patient had previously been in the habit of injecting laudanum.
So I regard historical research as more of a personal moral obligation than anything which appears to affect the saleability of books or their critical acclaim, more's the pity.
On the subject at hand, there are plenty of indigenous british plants the author could have used, given the slightest tendency to do research. I'm told angelica, while delightful candied, can give you a very nasty rash in the wild.