Dogs Mercury - Mercurialis perennis

Scientific Name: Mercurialis perennis. 'Mercurialis' means pertaining to the god Mercury, who revealed the 'medicinal' properties of the genus Mercurialis. 'Perennis' = perennial (there is an Annual Mercury too, M. annua).

English Name: Dogs Mercury. Any plant prefixed by the term 'Dogs' is a plant long considered useless medicinally. In this case the term more properly indicates that the plant is actually harmful if used medicinally. Also Snakes Flower, Snakeweed and Boggart Posy - all names that indicate that it is poisonous (a boggart is a malevolent household spirit).

French Name: La Mercuriale vivace (='perennial mercury'), mercuriale pérenne,(='perennial mercury'), chou de chien (= 'dogs cabbage'), cynocrambe.

5 Key Characters:
  • one of the earliest plants to emerge in the new year, sending out new shoots in January.
  • a plant of damp shady places.
  • flowers inconspicuous (plants are male or female, with different flowers depending on sex).
  • 15 - 40 cm tall.
  • unbranched stems with pairs of opposite oval leaves with small teeth.
Lookalikes: Enchanters Nightshade Circaea lutetiana.

Habitat: Mainly woods on basic or calcareous soil, but it can exist in a wide range of soil pH, from quite acidic to fairly alkaline. It rarely occurs on peat or sand, but is abundant on lime rich clay and loam so long as they are not prone to waterlogging. It is particularly shade tolerant and can form dense stands of up to 500 shoots per square metre in undisturbed woodland and exclude all competitors. In areas with more light it shares the forest floor with Bramble Rubus fruticosus agg., Rosebay Willowherb Chamerion angustifolium, Bluebell Hyacinthoides non-scripta, Enchanters Nightshade Circaea lutetiana, Primrose Primula vulgaris, Male Fern Dryopteris felix-mas, Herb Robert Geranium robertianum and False Oat Grass Arrhenatherum elatius. Female plants are more abundant in low light conditions, male plants more abundant in more intense light.

Flowering Period: January-February-March-April-May. The seeds are attractive to ants, bullfinches and greenfinches. Various hoverflies, moths, beetles and slugs visit the flowers or eat the leaves regularly.

Status: Widespread and locally common i.e. it is abundant at many scattered sites, but does not occur at many other places. Curiously, on the one hand it is seen as an indicator of ancient forest habitat, and on the other hand it is capable of tolerating high levels of heavy metal contamination in the soil. It is sensitive to disturbance by forestry activity, as well as trampling and grazing by deer. Stands of Dogs Mercury are long lived, but as they reproduce via rhizome extension, they are slow to (re)colonise new areas. The species has declined in abundance since the 1950s due to habitat disturbance.

Photographed by Loire Valley Nature:

Photographs are numbered from left to right and top to bottom. 1 a dense stand in well managed mixed forest on a limestone ridge near Preuilly-sur-Claise, April.

No comments:

Post a Comment