Dog’s Mercury is dioecious, meaning that there are separate male and female plants.
The male plant carries spikes of flowers that open to reveal between eight and fifteen, pollen producing, stamens.
Similar species: The leaves and flowers of Annual Mercury (Mercurialis annua) look very similar to Dog’s Mercury, the big difference between the species is that Annual Mercury grows on branched stems, by this I mean that they grow on stems which branch off the main stem.
I don’t have pictures of Annual Mercury because in the UK, it only grows in the South East of England but if you are unsure of your identification then just Google for images of Annual Mercury and look at the stem.
Dog’s Mercury is extremely poisonous. The first recorded case of fatality comes from 1693 when a family of five ate it and one child subsequently died. They had boiled the plant before eating it. The most recent case of poisoning comes from the 1980’s and was reported in The British Medical Journal. A couple boiled and ate the plant, mistaking it for an edible. They were hospitalised for two days but recovered without any serious ill effects. Their recovery was put down to the fact that they had boiled the plant before eating it.
Serious cases of poisoning in Humans are rare because there is little reason why anyone would eat this plant, most cases must arise from mistaken identity, or just not noticing the leaves when you pick your Wild Garlic.
Poisoning is more common in animals with several cases of Sheep poisoning being reported. I have also read a lot of reports of Dogs being drawn to eat it and subsequent vomiting. The plant has an unpleasant smell that repels us but may attract Dogs.
Dog’s Mercury in January:
Species: Mercurialis perennis