Dog's Mercury is an extremely poisonous plant found in deciduous woods and hedgerows. It also grows on some areas of limestone pavement. The common name arose because this plant was generally considered to be of little or no worth.
This perennial plant is common and widespread in woodlands in southern England and Wales but much less so in Scotland and Ireland. It spreads at a considerable pace and, as a result, often crowds-out other (more attractive) woodland species. This plant is also present throughout much of northern and central Europe including Slovenia.
Annual mercury is a weed that grows among crops in fields; it is very similar in appearance but it is not a perennial plant.
The Dopg's Mercury plants shown on this page were photographed in woodlands in West Wales.