Dog's mercury and the perils of colloquial plant names

 

Everyone looks forward to finding the first primroses, violets and bluebells blooming in spring, but the flowering of dog’s mercury Mercurialis perennis never gets a round of applause. But what it lacks in beauty, it makes up for with ecological gravitas and toxicity.

Dog’s mercury is common in woodlands almost everywhere and spreads via an underground rhizome, so large patches tend to be good indicators of very old woodlands and hedgerows. There are separate male and female plants, with the former being rather more common. This is a male plant, with stamens protruding from the tiny flowers.

Old colloquial plant names, like mercury, can lead to potentially dangerous confusion. The pot herb Good King Henry Chenopodium bonus-henricus also goes by the old name of English mercury and it is edible but dog’s mercury is most definitely poisonous. John Gerard, referring to it as French mercury in his herbal of 1597, seems to have confused the two, which may be why he wrote that it ‘cleanse and scour away the excrements and other filth contained in the guts. It serveth to purge the belly, being eaten or otherwise taken, voiding out of the belly not only the excrements, but also phlegm and choler.’