Annual mercury
Other names
Town weed
Latin names
Mercurialis annua
Weed Type
Annual Broad-leaved Weeds
Occurrence
An annual weed, possibly native on cultivated land and waste places. It is also a garden weed and is widespread but local in southern England. Although of local occurrence it can be troublesome on lighter soils. It is not recorded above 1,000 ft in the UK.
Annual mercury was found in 3% of conventional sugar beet crops surveyed in East Anglia in autumn 1998.
Annual mercury is rich in potassium and was regarded as a valuable purgative.
The plant is poisonous if eaten by livestock. The seeds are the most poisonous part but are important in the diet of bullfinches.
Biology
Annual mercury flowers from July to October. The male and female flowers are found on separate plants. Plants can be found in fruit for 4 months of the year.
In the field, seed germination occurs intermittently from May to early September.
Mineral uptake at early growth stages is relatively high, an important factor in plant competition.
Persistence and Spread
Seeds can remain viable in soil for 6-7 years. Seed longevity in dry storage is generally 8-10 years but seed dry-stored for 40 years has given 1% germination.
Seeds are dispersed explosively. Fallen seeds may be carried away by ants.
Management
Normal soil cultivations should keep the weed in check.
Annual mercury seed is susceptible to soil solarization.
Updated October 2007.