COMMON SIGHT: Dog’s mercury is a common sight in woods around Barney
COMMON SIGHT: Dog’s mercury is a common sight in woods around Barney

Dog's Mercury (Mercurialis perennis)
WHY is it called dog's mercury when it has nothing to do with dogs (except for poisoning them)?
In fact, dog’s in this sense means “false” or “bogus” – ie not the real mercury.
That is an edible plant called Good-king-Henry, provided in mythology by the god Mercury.
Dog’s mercury is one of the most common plants in deciduous woods, particularly beechwoods – so ubiquitous that you may not even notice the nettle-like 15 inch high stems (hence the confusion with Good-king-Henry).
Underground lurks a vast carpet of rhizomes that give the colonies their persistence and longevity.
These perennial plants are around almost all year but can suddenly disappear in late winter, leaving only a carpet of leaves.
Then, in late February, the bright green shoots seem almost to start from the leaf mould bearing ready-made flowers.
There are male and female plants, and after pollination occurs, seed is set in pea-sized fruits long before the trees sprout leaves. So this clever plant goes through its entire life cycle while the light is unshaded and bright.
These precocious flowers are a valuable source of nutrition for early emerging insects when little else is around to sustain them.
The ancient Greeks were familiar with dog's mercury, even giving male and female plants separate names.
They were used by both Hippocrates and Theophrastus, so obviously in herbal preparations the diluted extracts were deemed beneficial rather than toxic.
The poisonous factor is a chemical related to methylamine, a gas that causes vomiting and diarrhoea among other distressing symptoms.
Richard Mabey, in Flora Britannica, told of a Shropshire family who in 1693 cooked and ate dog’s mercury mistaking it for Good-king-Henry.
“The woman ... gathered some herbs and having first boiled them, fryed them with bacon for her family supper: after but two hours in bed the children fell very sick, which obliged the man and his wife to rise and take them to the fire where they vomited and purged, and within half an hour fell fast asleep. All went to bed and fell faster asleep than ever they had before. The man waked next morning three hours after his usual time, and went to his labour.
“He felt his chin had been all day by the fire and was obliged to keep his hat full of water by him all day long, and frequently dipped his chin in it.” One of the children died.
Barney woods are full of this stuff, so if home schooling has been too much for you...
Dr Richard Warren is a botanist living in Barnard Castle