Dog's Mercury Mercurialis perennis is a familiar plant of the spurge family (Euphorbiaceae) occurring in mostly shady habitats throughout Great Britain. There are records of the fruit and pollen of Dog's Mercury from deposits from the Hoxnian interglacial (425,000-375,000 BP) through the Bronze Age (5310-3210 BP) (Jefferson 2008), while the first historical record of the plant in Great Britain is for 1597, in Kent.