Mercurialis annua

Spurge Family [Euphorbiaceae]

month8apr month8april month8may month8jun month8june month8jul month8july month8aug


Date unknown Photo: © Bastiaan Brak
 Grows from 10 to 50cm tall. Leaves 1.5 to 5cm long, hairless and with 8 to 18 blunt teeth each side.

20th Aug 2011, Bowcombe, Isle of Wight. Photo: (CC by 2.0) Geoff Toone
 Erect and un-like Dog's Mercury, the stem is usually branched. It is dioecious like Dog's Mercury with separate plants being either male or female; this one has male flowers.

4th June 2011, Gallows Hill, IOW. Photo: (CC by 2.0) Geoff Toone
 Whereas, with fruit (tucked close to leaf axils near the stem) this one must be a female plant.

4th June 2011, Gallows Hill, IOW. Photo: (CC by 2.0) Geoff Toone
  The fruit are hairy and dumbbell shaped, but are larger than the fruit of Dog's Mercury.

10th June 2008, Bowcombe, IOW. Photo: (CC by 2.0) Geoff Toone
 Male flowers are more numerous than the female flowers and have numerous stamens with pale-green turning cream anthers. There are three sepals.

Date unknown Photo: © Bastiaan Brak
 The female flowers are in almost stalkless groups of 1 to 3.

Date unknown Photo: © Bastiaan Brak
 It is unknown how many female flowers (styles and stigmas) are clustered here, but anywhere between 1 to 3 is likely.

20th Aug 2011, Bowcombe, Isle of Wight. Photo: (CC by 2.0) Geoff Toone
 The fruits of a female plant. The leaves are bluntly-toothed (with 8-18 teeth per edge) [whereas the leaves of Dog's Mercury have 10-40 teeth each edge] and hairless. Leaves (at just 1.5 - 5cm long) are usually shorter than the 3-8cm long ones of Dog's Mercury.

20th Aug 2011, Bowcombe, Isle of Wight. Photo: (CC by 2.0) Geoff Toone
The fruits at 3 to 4mm across, are smaller than the 6-8mm across of Dog's Mercury. The fruits have small conical pimples each tipped by a hair (rounded pimples on Dog's Mercury).

Date unknown Photo: © Bastiaan Brak
 Leaves shiny, hairless and with 8-18 blunt teeth.

Not to be semantically confused with :   Mercury (  hydrargyrum) [a poisonous heavy metal chemical element].

No relation to : any of the Dog-violets (Viola), Dog Rose (Rosa canina) species, Crested Dogstail (Cynosurus cristatus), or any of the Dogwoods (Cornus) species [plants with similar names from disparate families].

Does not contain: Mercury, a toxic heavy metal.

Easily mis-identified as : Dog's Mercury (Mercurialis perennis) which differs from Annual Mercury in being in-branched, having hairs and the leaves are also usually a darker green and it grows in extensive carpets instead of singly on bare ground. The flowers are also slightly different. Whereas Annual Mercury grows mostly in the South and East, Dog's Mercury occurs throughout the UK. Other than those characteristics, the two are very similar.

Annual Mercury does not grow in large patches and unlike Dog's Mercury avoids limestone pavements, preferring disturbed ground such as gardens and arable land, other waste ground especially on light soils, also beaches.

Easily confused with : Dog's Mercury but that is not branched as is Annual Mercury, nor is it light green but a darker green.

It is (mostly) dioecious, with male flowers and female flowers on separate plants, but can also be androdioecious (with male flowers on some plants, and bisexual ones on others). The carpets are usually wholly of one sex or the other, but it doesn't need to be fertilised to spread by underground rhizomes.

Being a member of the Spurge family, although not a typical euphorb, it is toxic. When the stem is broken the sap (which un-like those from the Genera Euphorbia is not milky) can cause an allergic skin reaction. it is also hepatotoxic if eaten, causing liver damage. Of some 400 sheep which grazed upon this plant, 14 died of haemolytic anaemia (due to kidney and liver poisoning), the symptoms being diarrhoea, dullness, haemolytic anaemia and red urine (which is not due to blood, but rather to a red colouring in the plant). The reddish colour is due to a substance once named Mercurialine (now called methylamine,) which appears not to be toxic. Before the flowering stage, fresh plant material has a gentle laxative effect. The dried plant is almost in-active.

Both methylamine CH3NH2 and trimethylamine (CH3)NH2, which are volatile, are found in Annual Mercury. Trimethylamine is flammable and is found in fish, and has a strong 'fishy' odour as does methylamine. It is a common decomposition product of both animals and plants.

It is not as poisonous as its only other close relative, Dog's Mercury (Mercurialis perennis) which is a perennial rather than an annual.


Both Dog's Mercury and Annual Mercury contain a chromogen which is a piperidine alkaloid, hermidin. Hermidine is a powerful reducing agent, and as a solution in water exists in equilibrium with a tautomeric form: 3,6-dihydroxy-4-methoxy-1-methyl-pyridinone.

Hermidine in solution is colourless, but on exposure to air (oxygen) turns first blue, then on further exposure turns through green to yellow-brown. The blue derivative is called CyanoHermidin whilst the yellow-brown derivative is called ChrysoHermidin. These observations were made in 1925, when it was virtually impossible to determine the chemical structure of hermidin(e), least of all because of its propensity to change on exposure to air. Nowadays it has been determined that Hermidin is 5-hydroxy-4-methoxy-1-methylpyridine-2,6(1H,3H)-dione. Hermidin is most abundant in the roots of young and vigorously growing specimens, and exudes as a clear liquid, which turns first blue then green and finally yellow.

Hermidine is unstable in air forming hermidin dimers of which Hermidine quinone is one. Some of these are probably the blue and yellow-brown derivatives found in 1925. Three of these dimers are depicted here, there may be others. Confusion seems to be rife in these hermidin compounds. Much of the research into these compounds was done in the 1920's when analysis of by-products was not as easy nor as accurate as nowadays.

 This is called Hermidin Dimer A on the Dog's Mercury page and is yellow. Note the double-bond connecting the two halves, absent from the others.

 'Hermidin Quinone Dimer' is ChrysoHermidin mentioned above. It is yellowish-brown in colour.

PYOCYANIN, a blue pigment

  It has now been discovered that the blue derivative of Hermidin coincides with the blue pigment Pyocyanine found in the gram-negative bacterium Pseudomonas aeruginosa which is commonly found in soil and dirty water. Pseudomonas aeruginosa is an opportunist pathogen not only of mammals, where it is a huge problem in hospital acquired infections (similar to MRSA), but occasionally also of plants. Infected tissue takes on a characteristic blue hue, due to the pyocyanin. Unfortunately, your Author cannot find any further corroborative evidence for it being an actual constituent of Annual Mercury. It seems at least possible that this compound could also be one of the factors produced from the sap of plants of Genus Mercurialis. Pyocyanin is a toxic phenazine (or more correctly, a phenazinone) and blue pigment. It has anti-biotic properties against gram-positive bacteria (but not the gram-negative bacteria, within which it is found).


In the last 10 years another compound has been isolated from Annual Mercury: that of Isochrysohermidin. First of all, it will be noted it lacks the six-membered ring of Hermidin, and is instead a dimer of two five-membered rings (close inspection shows the relationship between hermidin and this compound, which at first glance is not obvious). Isochrysohermidin has the ability to form inter-strand DNA cross-links, which makes it potentially a toxic chemical that can put a spanner in the works of the genetic machinery. It seems that it has the ability to selectively target the C2 amine of Guanine, one of the amino acids in DNA. It has been shown that the yellow-brown substance described above is the dimeric oxidation product of hermidin: chrysohermidin.

Other volatile substances found in predominantly in the roots of plants of the genus Mercurialis are Benzyl Alcohol, 2-phenylethanol, 4-methoxyphenol, 3,4-dimethoxyphenol, myrtanol (both cis and trans forms), cis-myrtanal and squalene.

Annual Mercury also contains saponins, which are cytotoxic.

Of the two Mercury's, Dog's Mercury is the more poisonous, giving not just one but two distinct syndromes, the first being haemolytic anaemia (as for annual Mercury), the second being oedematous gastroenteritis.

  Mercurialis annua  ⇐ Global Aspect ⇒ Euphorbiaceae  

 family8Spurge family8Euphorbiaceae
 BSBI maps


Mercurialis annua

Spurge Family [Euphorbiaceae]

WildFlowerFinder Homepage