This plant is a Spear thistle Cirsium vulgare also known as the Bull or Common thistle, and the most likely candidate for the role of ‘National Flower of Scotland’, although this particular one is growing in Much Wenlock beside the allotment hedge. I’m not sure why the Scots particularly took thistles to heart (a prickly enterprise if ever there was one), though there are possibly clues (not always decipherable) in Hugh MacDiarmid’s 1926 epic stream of consciousness in which one features. It is called A Drunk Man Looks At A Thistle, and at 2,685 lines long, and written in Border Scots dialect, is a challenging read, though the version at the link above does provide a glossary here and there. Go there if you wish to discover some stunning Scots vocabulary.
Here are two tiny, rather more accessible excerpts, the first describing the thistle seen in the moonlight; the second likening it to the chief drone on a set of bagpipes:
The thistle canna vanish quite.
Inside a’ licht its shape maun glint,
A spirit wi’ a skeleton in’t.
Plant, what are you than? your leafs
Mind me o the pipes lod drone
– And aa your purply tops
Are the pirly-wirly notes
That gang staggerin ower them as they groan
And then this is what happens next, in my version of reality that is:
…a ‘pirly-wirly’ explosion of would-be thistles. Those floating seed heads get everywhere, making it yet another highly successful pest of farm fields and gardens. In its favour, the flowers are much loved by moths, butterflies and bees (as well as being most striking to look at) and birds, especially goldfinches, like to feed on the seeds.