A poisonous coloniser of ancient woodland, dog’s mercury is quick to sweep over the wood floor, sometimes outcompeting more delicate ancient woodland species.
Common names: dog’s mercury, false mercury, boggard posy, dog’s cole
Scientific name: Mercurialis perennis
Family: Euphorbiaceae
Origin: native
Flowering season: February to April
Habitat: ancient woodland, broadleaf woodland, hedgerows
A perennial, dog’s mercury is a medium-height woodland plant.
Leaves: large and long pointed oval-shaped leaves with toothed edges. They are bright green, hairy and crowded towards the top of the stem.
Flowers: are small and green. They flower in the spring.
Look out for: it covering the ground in ancient woodland.
Not to be confused with: species of Chenopodium. Dog’s mercury is unrelated, but similar to good-king Henry (Chenopodium bonus-henricus). The common name for this species is mercury, which gave dog’s mercury its name (the ‘dog’ meaning bad or not as good in reference to its poisonous properties).
The plant has an unpleasant decaying smell.
Dog’s mercury is not a showy plant and is easily overlooked, but it’s very common. It flourishes in woodland with a preference for living under oak, beech, ash and elm. Although it’s mainly a plant of ancient woods, it can colonise new deciduous woodland very quickly. It favours shady areas and can also be found in hedgerows.
Credit: Tim Smith / WTML
Some species of ground-nesting bird, such as woodcock, seem drawn to areas colonised with dog’s mercury. Speckled bush cricket nymphs feed on the leaves of dog’s mercury, along with other species including beetles, weevils, springtails and molluscs.
Credit: Alex Hyde / naturepl.com
The name dog’s mercury has nothing to do with the pet – the plant is toxic to many animals, including dogs. It actually refers to it looking similar to, but ‘lesser than’ plants in the mercury family.
Credit: David Chapman / Alamy Stock Photo
Dog’s mercury is an ancient woodland indicator. This means it can be used to determine if a wood is long-established, even in areas which no longer have tree cover. All parts of dog’s mercury are poisonous. It can induce jaundice, diarrhoea, vomiting and even death.
Ancient woodland is one of our rarest woodland habitats. Dog’s mercury is just one species that contributes to the biodiversity of ancient woods. Loss of these habitats threatens some of our rarest wildlife species.
Help us restore irreplaceable ancient woodland and bring it back to its former glory.
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