Devil's-bit Scabious

Succisa pratensis

in mid to late summer the blue button like flowers of this plant float 3’ high in marshes and wet places all over Britain. The association with the infernal one is somewhat convoluted but seems to refer to an act of spite on his part resulting in his chewing off the end of the root, which does have a rather mangled appearance.

Supplied as Bare-root Plants (sent without pots, with roots carefully prepared for planting)