Mercurialis perennis, commonly known as dog's mercury, is a poisonous woodland plant found in much of Europe as well as in Algeria, Iran, Turkey, and the Caucasus, but almost absent from Ireland, Orkney and Shetland. A member of the spurge family (Euphorbiaceae), it is a herbaceous, downy perennial with erect stems bearing simple, serrate leaves. The dioecious inflorescences are green, bearing inconspicuous flowers from February to April. It characteristically forms dense, extensive carpets on the floor of woodlands and beneath hedgerows. Growth and location Mercurialis perennis is a herbaceous plant. It usually grows in dense masses often in the ground flora of beech, oak, ash, elm and other types of woodlands in Europe. It also grows under the shade of hedgerows and scrub. It has a preference for moderately shady to densely shady habitats. It is able to colonize new deciduous woods on dry, calcareous soils at an annual rate of a meter or more. Under such conditions, the plants, especially the females, often display a darker green color. Its period of reproductive activity depends upon a number of factors such as illumination, soil reaction, soil moisture, etc. These factors also affect the duration of reproductive activity. Dog's mercury favors alkaline (basic) soils and can be found in abundance in suitable habitats in limestone regions. It also occurs widely on neutral soils but is absent from acidic ones. Spreading by underground rhizomes, where its dense growth may shade out other woodland flowers such as oxlip, fly orchid, and even young ash seedlings, but in the open, it eventually gives way to other plants. Mercurialis perennis extends from sea level to the mountain range. The ultimate height attained in different mountainous regions, e.g. in Scotland, England, Germany, and Switzerland, naturally varies with the latitude and other geographical factors. Existing colonies in some parts of Britain (including some in woods on boulder clay in East Anglia), are expanding and showing increased vigor, perhaps as a result of deeper shade in woodlands where coppicing has ceased. Names The plant's common name derives from the plant's resemblance to the unrelated Chenopodium bonus-henricus (Good King Henry, also known as mercury, markry, markery, Lincolnshire spinach). Since Mercurialis perennis is highly poisonous, it was named "dog's" mercury (in the sense of "false" or "bad"). It has also been known as boggard posy. Categorization There are separate male and female plants (the species is dioecious). the plants are