Dog’s Mercury is a common woodland plant in England and Wales as well as in mainland Europe and can also be found in South West Asia. It is poisonous and really should be avoided, although dogs seek it out their owners say and then vomit, so it is used by them as they use other grasses such as couch grass. Dog’s Mercury is a member of the spurge or Euphorbiaceae family of plants which includes Ricinis communis or the castor oil plant, cassava or manioc, and Croton tiglium or jamalgota among others.
Nicholas Culpeper, writing in the 17th century has this to say of it and certainly cautions against its use, chastising earlier herbalists for not doing the same: -
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Traditionally Dog’s mercury has been used in an ointment applied to external dressings for wounds, and it is said to soften and moisturize the skin. It has also been used to get rid of sores in the ears and around the eyes, but that was in the dim and distant past when other forms of medication were unavailable. It was used in ancient Greece as an antiseptic and to get rid of warts.
It smells rank and if you follow your nose, you will not be able to eat it, even if your body needs to be purged. This was its main use in the past, as it induces vomiting and diarrhoea.
It is even more noxious than French, annual or garden mercury, all names of the same plant, Mercurialis annua. For once it would be advisable to keep Culpeper’s advice in mind and stay clear of this plant.