Invasiveness Assessment - Annual mercury, mercury weed (Mecurialis annua) in Victoria

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Plant invasiveness is determined by evaluating a plant’s biological and ecological characteristics against criteria that encompass establishment requirements, growth rate and competitive ability, methods of reproduction, and dispersal mechanisms.

Each characteristic, or criterion, is assessed against a list of intensity ratings. Depending upon information found, a rating of Low, Medium Low, Medium High or High is assigned to that criterion. Where no data is available to answer a criterion, a rating of medium (M) is applied. A description of the invasiveness criteria and intensity ratings used in this process can be viewed here.

The following table provides information on the invasiveness of Annual mercury.

A more detailed description of the methodology of the Victorian Weed Risk Assessment (WRA) method can be viewed below:

Victorian Weed Risk Assessment (WRA) method (PDF - 630 KB)
Victorian Weed Risk Assessment (WRA) method (DOC - 1026 KB)
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Common Name: Annual mercury
Scientific name: Mecurialis annua

Question	Comments	Rating	Confidence
Establishment
Germination requirements?	An annual, the plant can be propagated by seed sown in spring or autumn (PFAF 2003). Optimum temperature for germination is constant 20 or 25°C (Anderson 1968). Lisci et al. (1994) note that M. annua flowers all year round in southern and central Italy, hence pollination and seed production would occur throughout the year. They do not report on seed dormancy. As a weed in sugar beet crops Jursik et al. (2004) noted there were several waves of emergence, influenced by weather conditions. Seedling emergence began at the end of April and progressively increased to a maximum in June (northern hemisphere summer). Germination had mostly ceased by November. Magyar and Hunyadi (2000) record temperature as the main factor regulating germination of M. annua. Magyar (2003) states, “It can be observed that the germination of annual mercury seeds has a seasonal pattern under natural field conditions.” Natural seasonal disturbance.	MH	H
Establishment requirements?	Common habitats are gardens, arable land, vineyards; rubbish tips; on soils rich in nutrients, in light and moderately warm situations up to montane level. In California it is noted as a weed of agriculture in disturbed habitats (CALFLORA 2007). In Hungary, where the weed has significantly extended it area of infestation, it is mostly known in cropping situations (maize and winter wheat, sugar beet and carrot) and ruderal areas (Magyar 2003). Requires open space or bare ground to establish	L	H
How much disturbance is required?	In some areas of Europe (Hungary, Czech Republic) it is more common in arable land used for annual cropping activities (Magyar 2003). Infestations most commonly occur in highly disturbed environments. See above.	L	H
Growth/Competitive
Life form?	Annual herb, 10–40 cm high. ‘Other’ life form.	L	H
Allelopathic properties?	Magyar (2003) found allelopathic potential against three species; amaranth, white mustard and wheat. In wheat, only the early growth of seedlings was affected; germination was not inhibited. Magyar’s conclusion was that, “The proven allelopathic potential of annual mercury as a part of the interference can contribute to its further expansion on arable lands.”	MH	H
Tolerates herb pressure?	The plant is consumed by grazing animals, but the plants are known for, “high seed production and longevity.” Reproduction may be inhibited by herbivory, but extensive seed bank would ensure weed persists. Yampolsky (1930) found that heavily pruned plants of M. annua recovered and subsequently produced flowers and seed. (Note: some of the male-only plants produced a few female and hermaphrodite flowers after pruning.)	MH	MH
Normal growth rate?	Magyar & Hunyadi (2000) state, “The high relative growth rate values during early development indicate the strong competitive nature of this weed,” but this is contradicted by Magyar (2003) and Jursik et al. (2004) who suggest it is less competitive particularly in relation to other species of primary weed infestations. Growth rate likely to be less than other species of same life form.	ML	H
Stress tolerance to frost, drought, w/logg, sal. etc?	The plant is, “frost resistant but drought tender,” (Bodkin 1990). An annual, the plant would not tolerate fire. No data on response to water logging. Resistant to one stressor, susceptible to at least two.	L	M
Reproduction
Reproductive system	An annual; dioecious (male and female flowers borne on separate plants). M. annua is known to produce both functional males and hermaphrodites under some conditions. Under experimental conditions, Yampolsky (1930) found the same male-only plant can produce female and hermaphrodite flowers during recovery from deliberate damage (pruning). Pannel et al. (2003) demonstrate also that under the influence of ecological interactions populations of M. annua can be dioecious, androdioecious (males and hermaphrodites) and functional hermaphroditism. It has been suggested that species of Mecurialis are out-crossers.	L	H
Number of propagules produced?	Jursik et al. (2004) found that M. annua produces up to 20,000 seeds m^-2 in sugar beet stands. Propagules likely to exceed 2,000 per plant per flowering event.	H	H
Propagule longevity?	The plant has, “a long primary seed dormancy, …and longevity in soil,” (Kohout & Hamouz 2000) Specific values of percentage viability and longevity not available. Assume at least 25% of seed survives 5 to 10 years.	ML	L
Reproductive period?	Annual species.	L	H
Time to reproductive maturity?	An annual, the plant reaches maturity and produces viable propagules in under one year.	H	H
Dispersal
Number of mechanisms?	Lisci & Pacini (1997) report in a study from Italy, seed dispersal was observed to occur by two methods; explosive ejection and ants. Seeds were measured to be thrown up to 130 cm from the plant, while ants dispersed the seed up to 14 m. Seed ejection may result in population spreading quite rapidly. In Victoria, the plant is known to grow on a stream bank/drainage channel (Baber; Lorimer, pers. comms.). Ejection is likely to place seeds in the water body, but there is no data available on dispersal by water or seed buoyancy.		H
How far do they disperse?	Mean dispersal by seed ejection and ants is <5 m (Lisci & Pacini 1997). Very few to none will disperse to 1 kilometre, mostly confined to 5 metres or possibly further if the plant is on or near stream bank.		H

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