As a teenager I remember having a bit of a fondness for the story of The Scarlet Pimpernel. I'm not sure why, but it was one of my favorites, (along with the musical Guys and Dolls). I was recently reminded of this when my mom showed me a picture of a Scarlet Pimpernel flower she was thinking of drawing for her art class....it is a very pretty flower. I remember in the play and novel that the elusive Pimpernel would draw this flower when he left messages for his men, and I remember wondering "Why that flower?". Well, in looking a few things up, the best I came up with was from Wikipedia..
This common European plant is generally considered a weed and is an indicator of light soils.
But even so, did the writer know that? I honestly doubt it considering the play was written in 1903. None the less, I think it fits well enough. If I remember the story right, (it's only been about 15 years since I've read it), the English did consider "The Pimpernel" to be a weed, not realizing he was one of their own who was masquerading as a slow-witted and deficient individual. They couldn't see what he really was.
For those that don't know about it, here's a short little trailer I found. The first 30 seconds are a bit long, but otherwise.. (and I particularly like the poem).