I was very pleased to have refound the blue pimpernel by the track to the south of the old wood yard not far from the site where I first saw it maybe 20 years ago.
There are two 'blue pimpernels' in the British Isles, but they are very difficult to tell apart. Our common scarlet pimpernel (Anagallis arvensis subsp. arvensis) with, surprise, surprise, scarlet flowers has a blue form (wait for it) Anagallis arvensis subsp. arvensis forma azurea. The other one is Anagallis arvensis ssp. foemina. The defining difference is found in the small hairs along the outer edges of the petals. In A. a. a. azurea these hairs have three cells and the end one is globular. In A. a. foemina they have four cells and the end one is oval.
The cells do not, of course, have numbers engraved on them.
I looked, under a high power microscope, at a flower from Brede High Woods and another blue one from a colony that has been flourishing in our garden for ages and the one from the woods is the true blue pimpernel (A. a. subsp. foemina).
All this made me wonder what these microscopic hairs on the petals are for. The end cell in both species is reddish and glandular so I assume it contains some special chemical. What for? Perhaps if the plant is lightly crushed underfoot, the chemical is released and attracts potential pollinators, but this seems a rather complicated way to evolve to achieve an end much more easily achieved by other plants without such devices.
An ancient introduction, A. a. foemina, is now quite rare and according to the New Atlas of British and Irish Flora may be declining, probably due to more intensive weed control in arable fields, though some records may be from bird-seed.