A short to medium height plant with slender, unbranched, erect stems. Leaves elliptical to oblong, untoothed and usually hairless. Umbel usually 5 rayed with green bracts.  Flowers with rounded glands, green at first, but soon becoming dark purple.  A cultivar named 'Chamaeleon' has dark purple foliage.

Good quality photographs required.

Favours damp or shaded habitats, found naturalised in woodland and scrub, and on roadsides and river banks.

Flowers May to July.

A rhizomatous perennial herb.

Fairly widespread, although occasional, as a naturalised plant in Britain.

Rarely recorded in Leicestershire and Rutland.