The scarlet pimpernel, Anagallis arvensis, is generally considered to be a weed. Confusingly they can also have blue flowers. It is toxic to many grazing animals, though they tend to avoid it due to its bitter taste. It has been used in folk medicine to treat wounds and as an expectorant.
This simple little flower is perhaps more famous as the symbol of Sir Percy Blakeney. « The Scarlet Pimpernel » is the 1905 novel by Baroness Orczy detailing the exploits of the Scarlet Pimpernel (Blakeney), an English aristocrat who rescues French aristocrats from the cutting edge of French republicanism. Famous for his foppish refrains such as, “Odd’s fish, m’dear! The man can’t even tie his own cravat!” You can read the book for free here.