Title: Mercurialis annua L.

Scientific Name:

Mercurialis annua L.

Common Name:

annual Mercury

O

Source

Habitat: 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). Where it occurs north east of Melbourne (Victoria), it is most commonly associated with a creek corridor in a nature reserve, but is also known to be present in local gardens.

Distribution:



Original source via GBIF


Invasiveness Assessment

ESTABLISHMENT


1. 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.

2. 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

3. 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.

GROWTH / COMPETITIVE


4. Life form? Annual herb, 10–40 cm high. ‘Other’ life form.

5. Allelopathic properties? None described.

6. 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.)

7. 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.

8. 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.

REPRODUCTION


9. 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.

10. 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.

11. 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.

12. Reproductive period? Annual species.

13. Time to reproductive maturity? An annual, the plant reaches maturity and produces viable propagules in under one year.

DISPERSAL


14. 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.

15. 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.


Impact Assessment

RECREATION


1. Restrict human access? Annual herb 10 – 40 cm high. In Western Australia, it is recorded to reach a height of 60 cm (Hussey et al. 1997).
Negligible impact on human access

2. Reduce tourism? An introduced species to North America, it is known in San Francisco in open, disturbed areas, fields and roadsides. Where it occurs north east of Melbourne (Victoria), it is most commonly associated with a creek corridor in a nature reserve, but is also known to be present in local gardens. Infestations likely to be undetectable to the average visitor.

3. Injurious to people? Vallverdu et al. (1997) demonstrated a high level (46.4%) of sensitisation to pollen of M. annua in subjects with a known sensitivity to other pollens. Lisci et al. (1994) records that M. annua is a wind-pollinated plant and produces pollen throughout the year in central and southern Italy. Rossof (2002) reinforces the allergenicity of this plant in Italy where, he states, its aeroallergens have caused rhinitis, bronchial asthma, and/or hypersensitivity pneumonitis in humans. “Use of it colors urine red.” Neat huh! Potential to cause allergic reaction or increase the duration of suffering for those susceptible to pollen allergies

4. Damage to cultural sites? Low growing annual herb. Dense patches may create a moderate negative visual effect.

ABIOTIC


5. Impact flow? Although it is found near to streams and drains in Victoria, it is a terrestrial species. No impact on water flow.

6. Impact water quality? See comment above. No data is available to indicate the water stress-tolerance of this plant. Assume it unlikely to establish in standing water.

7. Increase soil erosion? A soft annual herb more commonly found in disturbed or ruderal situations. Its presence is unlikely to affect soil erosion.

8. Reduce biomass? In natural ecosystems it is commonly found in disturbed sites or waste places (CALFLORA 2007; Magyar 2003). Biomass may increase slightly, but likely little to no effect.

9. Change fire regime? Small, fleshy annual herb. Even dense patches are unlikely to add significantly to fuel load. Little to no affect on fire intensity or frequency

COMMUNITY HABITAT


10(a) Impact on composition of high value EVC? EVC=Valley Grassy Forest (V); CMA=Port Phillip; Bioreg=Gippsland Plain; CLIMATE potential=VH. Occurs along creek / drain line north east of Melbourne where it is displacing other herbaceous annuals and, as a prolific seeding annual, spreading quickly in the absence of control. It is difficult to comment on the level of displacement (minor or major) this species may impose on the lower stratum. Somewhere in the middle?

10(b) Impact on medium value EVC? EVC=Coastal Headland Scrub (D); CMA=Port Phillip; Bioreg=Gippsland Plain; CLIMATE potential=VH. A soft, annual herb. Impact similar to 10. above.

10(c) Impact on low value EVC? EVC=Riparian scrum (LC); CMA=West Gippsland; Bioreg=Wilsons Promontory; CLIMATE potential=VH. A soft, annual herb. Impact similar to 10. above.

11. Impact on structure? Known in peppermint woodland at Hamelin Bay, Western Australia (about 35 km south of Margaret River), but no detail on effect of its presence on other vegetation. Where it occurs near Melbourne, Victoria, it is associated with a creek corridor / drain in a nature reserve (Baber; Lorimer, pers. comms) where it is displacing other more desirable annual herbs. Minor impact on lower stratum.

12. Effect on threatened flora? Not documented.

FAUNA


13. Effect on threatened fauna? Effects not known. At present in Victoria it is likely that the habitats of annual mercury and threatened fauna are mutually exclusive.

14. Effect on non-threatened fauna? Displacement of beneficial plants by M. annua may lead to a reduction in available fodder for non-threatened species.

15. Benefits fauna? Provides no documented benefit. It is recorded as poisonous to domesticated animals (sheep, cattle and horses (Rossof, 2002)). See comments below.

16. Injurious to fauna? Welchman et al. (1995) and Deprez et al. (1996) report the poisoning of lambs and cattle respectively. 11 lambs died, but the life outcome of the cattle is not described. In the case of lamb poisoning, the authors noted that annual mercury was the predominant vegetation. Rossof (2002) indicates that annual mercury is lethal to all domestic animals (sheep, cattle, horses). Though animals may avoid eating the plant, the potential exists to fatally harm fauna at certain times of the year

PEST ANIMAL


17. Food source to pests? Probably unlikely; see comments in 16 above. Pest herbivores may find consuming this plant to be fatal.

18. Provides harbor? Images of infestations in California (CalPhotos) show the plant would not provide harbour for pest animals.

AGRICULTURE


19. Impact yield? Although reported as toxic to domesticated animals no data exists on effects on yield regarding stock. Magyar (2003) has undertaken the most comprehensive study of this plant to date, though with a focus on agricultural ecosystems, notably annual crops such as maize and winter wheat. He found that the average cover in maize varied from 1.16% to 2.28%. How it affected production and yield is not discussed. The major concern was the emergence of the weed before the cultivated crop. Given this early competition for plant resources, it could result in a reduction in crop yield of more than 5%, but less than 20%.

20. Impact quality? There are no data available to suggest the quality of agricultural produce is affected. The few studies on animals consuming the plant (Rossof 2002; Welchman et al. 1995; Deprez et al.1996) suggest that mortality is the most likely outcome rather than a reduction in vigour. It is not recorded as a seed contaminant. No impact on quality.

21. Affect land values? The continuous spread of this weed in north-western Hungary (Magyar 2003) in annual crops indicates it has been a difficult weed to control or possibly just ignored as another weedy crop competitor. Magyar (2003) demonstrates effective control of annual mercury with herbicides. Normal farm / crop management practices would likely control the weed, though possibly adding to the cost of production. Unlikely to affect land value.

22. Change land use? See comment in 21 above regarding cropping situations. As the weed is most closely associated with high disturbance regimes, well maintained, good quality perennial pasture is likely to suppress the growth of annual mercury. Unlikely to lead to change in land use.

23. Increase harvest costs? Not demonstrated to affect harvest costs.

24. Disease host/vector? Not documented.




Feedback

Do you have additional information about this plant that will improve the quality of the assessment? If so, we would value your contribution.


Assessment ratings originally made by the Victorian Department of Primary Industries.
The entry of this assessment was made possible through the generous support of The Weed's Network.






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Date: 21 November 2011; 2:02:34 PM AEDT

Author Name: David Low
Author ID: adminDavid