Medium to tall, hairy, faintly aromatic plant to 2 metres, stems erect. Leaves oblong to lanceolate with a heart shaped base, blunt toothed, only the lower stalked, the upper unstalked. Flowers purple, 12 to 15 mm long, the whorls forming a dense spike interrupted below.

Damp habitats, margins of ponds, rivers and canals, but also on disturbed ground and cultivated fields.

June to October.

Perennial.

Fairly frequent throughout most of Britain except for the Scottish Highlands.

Fairly frequent in Leicestershire and Rutland. In the 1979 Flora survey of Leicestershire it was found in 63 of the 617 tetrads.