One reason may be this:
Sir Percy
Scarlet Pimpernel
I understand in the first draft he was known as the red carnation. A scarlet pimpernel is a common hedgerow flower in England. Scarlet sounds more romantic than red, pimpernel has a lovely sound, I think it was a good choice to change it!
Anagallis arvensis is the latin name for the flower.
little edit
He also puts scarlet pimpernels on his notes :D