A low, bright green carpet in late winter, each unbranched stem topped by toothed oval leaves in pairs and tiny petal-less green flowers
Dog's mercury — one of the earliest woodland flowers, blooming from February.
Nature · Wildflowers & flowers
Dog's mercury
Native · flowers Feb–Apr · ancient woodland and shady hedge banks
Mercurialis perennis — Euphorbiaceae
Dog's mercury is a low, unshowy, poisonous perennial that carpets the floor of old woods in late winter, long before the canopy closes. Its tiny green flowers are easily overlooked, but a wood full of it is a good clue that the woodland is ancient. It flowers earlier than almost anything else on a woodland walk, so it opens the seasonal sequence of the wood and the lane.
How to spot them
- ▸Dense, patchy carpets of unbranched stems with pairs of bright green, toothed, pointed-oval leaves crowded towards the top
- ▸Flowers are tiny and green with no petals; male and female flowers grow on separate plants
- ▸Leaves and stems are softly hairy and smell unpleasant when bruised
- ▸Look-alike: good-king-Henry (Chenopodium bonus-henricus) is unrelated and grows in open, disturbed ground; dog's mercury is a shade-lover with paired, toothed, hairy leaves
- ▸A thick carpet of it under oak, beech, ash or elm is a classic ancient-woodland indicator
How to know it
Every part of this woodland carpet is poisonous, and the 'dog' in its name means worthless rather than referring to pets
Dog's mercury — 'dog' meaning bad or inferior to the true mercury.
A dense, continuous sward of this species under oak and ash is read by ecologists as a sign that a wood has stood for centuries
Dog's mercury — an ancient woodland indicator.
Male and female flowers of this spring woodland plant grow on separate plants, and it belongs to the spurge family
Dog's mercury is dioecious — family Euphorbiaceae.
Bruise the leaves of this hairy, bright green woodland plant and the smell is decidedly unpleasant
Dog's mercury — the Woodland Trust notes an unpleasant decaying smell.
Nymphs of the speckled bush cricket feed on this poisonous woodland ground cover, and woodcock seem drawn to patches of it
Dog's mercury — the Woodland Trust lists these visitors.
Folk names for this poisonous ancient-woodland plant include boggard posy, false mercury and dog's cole
Dog's mercury.
Quick-fire facts
- •Family Euphorbiaceae, the spurge family
- •Flowering season February to April, according to the Woodland Trust — among the first woodland wildflowers of the year
- •All parts are poisonous to people and animals, including dogs; the Woodland Trust says it can cause jaundice, diarrhoea, vomiting and even death
- •An ancient woodland indicator: a slow coloniser in general, though the Woodland Trust notes it can spread into new deciduous woodland quite quickly
- •Dioecious — male and female flowers grow on separate plants, so a patch may be all one sex
- •'Dog's' means 'lesser than' or worthless: the plant resembles good-king-Henry, also called mercury, but is poisonous
- •Grows with bluebell and wood anemone in old woodland, and is also found in shady hedgerows
- •It can form such dense carpets that it outcompetes more delicate ancient woodland species, notes the Woodland Trust
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Sources
- Woodland Trust — Dog's mercury (Mercurialis perennis)