Verbena bonariensis.

Lots of this plant flowering at the allotment site at the moment and stays flowering for some time.  Sways beautifully when combined with grasses in a light breeze which we had today.  Lovely sunny interlude for a dog walk with  friend in Belfairs Woods.  My friend's dog went for a little dip in the brook which looked so much fun that Ginny followed.  I have a feeling she's going to be a swimmer.  Water only a trickle at this accessible spot so she didn't actually float.