In recent centuries, annual mercury has spread to northern Europe and many other parts of the world as an agricultural and urban weed.

Male plants have their flowers arranged at the tips of long stalks (peduncles) arising from the leaf axils and projecting beyond the leaves.

Female plants have their flowers in sessile clusters of 1-4 at the nodes of the branches, or on short (4 mm) pedicels if attached to the main stem.

The original name is still used today, but several synonyms have been coined over the years, including Mercurialis ambigua L.f. (1762), Discoplis serrata Raf.

In parts of southern Europe and north Africa, however, plants are sometimes tetraploid, hexaploid, or have even higher levels of ploidy, and it is also in these areas that monoecy, androdioecy and gynodioecy occur.

Richard Mabey claims that the "true" mercuries are goosefoots, specifically Chenopodium bonus-henricus, and that the name became attached to this genus because of a superficial resemblance between them.

[16] Dioscorides[15] used the Ancient Greek name "linozostis" and said it was called by the Romans herba Mercurialis mascula or M. testiculata; and by the Egyptians aphlopho.

Annual mercury is native to the Middle East and countries bordering the Mediterranean Sea, where it occurs in desert and semi-arid regions, and from which it has spread to disturbed, agricultural soils and urban areas around the world.

[19] In Britain, it occurs mainly in the south and east[20] but has spread north in the latter half of the 20th century, becoming roughly three times as widespread.

When these seeds land, the vibration caused by the impact attracts harvester ants of the genus Messor (in Italy, the species M. structor) which immediately gather them up and transport them to their nests, up to 5 m away.

With the caruncle removed, the seeds are ready to germinate, but they will not do so until the third stage occurs, when the ant nest is destroyed by some external event such as animal disturbance, flood, or ploughing.

For this reason, annual mercury is especially common in agricultural land, where it behaves not as a ruderal colonist of bare ground, but as a specialised inhabitant of places with regular disturbance events.

[24][9] The habitats it grows in include Eastern Mediterranean limestone screes (Eunis code H2.68), on old walls (J1.31), and on disturbed soils in little robin-hairy bittercress, nettle-leaved goosefoot, and hedge mustard vegetation communities.

[25][8] Here it often grows at the base of walls where there also a rich supply of nutrients, along with such plants as black horehound, common mallow and hedge mustard.

[26] Subsequently, it spreads to arable fields and waste ground, and it is described in the National Vegetation Classification as occurring in OV6 sticky mouse-ear, OV9 scentless mayweed and OV13 chickweed communities.

[28] Although it is generally thought to be wind-pollinated, male annual mercury plants can produce tens of thousands of flowers in a growing season, and these give rise to vast quantities of pollen and nectar.

[30] Another rust-like infection is caused by Synchytrium mercurialis (Libert) Fuckel, 1870, which produce glassy, golden warts and can distort the leaves.

and Kalcapion semivittatum (Gyllenhal, 1833), whose larvae cause a large, oval swelling inside the stem or the petiole, and the buckthorn aphid Aphis nasturtii Kaltenbach II.

The closely related dog's mercury certainly is, as there are cases where people have mistaken it for an edible herb such as spinach, and subsequently died.