Medicago polymorpha (bur clover)
- Summary of Invasiveness
- Taxonomic Tree
- Notes on Taxonomy and Nomenclature
- Distribution Table
- History of Introduction and Spread
- Risk of Introduction
- Habitat List
- Biology and Ecology
- Air Temperature
- Natural enemies
- Notes on Natural Enemies
- Means of Movement and Dispersal
- Plant Trade
- Impact Summary
- Economic Impact
- Environmental Impact
- Social Impact
- Risk and Impact Factors
- Similarities to Other Species/Conditions
- Prevention and Control
- Distribution Maps
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PicturesTop of page
IdentityTop of page
Preferred Scientific Name
- Medicago polymorpha L.
Preferred Common Name
- bur clover
Other Scientific Names
- Medicago apiculata Willd.
- Medicago denticulata Willd.
- Medicago hispida Gaertn.
- Medicago lappacea Desr.
- Medicago nigra (L.) Krock.
- Medicago polycarpa Willd.
- Medicago reticulata Benth.
International Common Names
- English: bur medic; bur trefoil; burclover; burr medic; burr medick; hairy medic; rough medic; rough medick; toothed bur-clover; toothed medic; trefoil-clover
- Spanish: carreton de amores; trébol de carretilla; trefol de carretilla
- French: luzerne hérissée; luzerne hispide
- Arabic: Nafal
- Chinese: nan mu xu
- Portuguese: carrapico
Local Common Names
- Australia: bur medick
- Bolivia: alfalfilla
- Colombia: rodajilla
- Germany: Borsten-Schneckenklee; Gezähnter Schneckenklee; Rauhe Luzerne; Rauher Schneckenklee; Steifhaariger Schneckenklee
- Honduras: caretilla
- Italy: medica ispida
- Japan: umagoyashi; uma-goyashi
- Korea, Republic of: gaejari
- Netherlands: ruiger rupsklaver
- Nicaragua: cadillo de vaca
- Sweden: tagglusern
- UK: hairy medick; toothed medick
- USA: California burclover; California bur-clover
- MEDPO (Medicago polymorpha)
Summary of InvasivenessTop of page
Medicago polymorpha is a herbaceous legume that is native to western and central Asia and countries around the Mediterranean, and has been introduced widely around the world. It is found in particular in regions with a Mediterranean climate, but is by no means confined to them. Introduction has been a result of accidental transport of the spiny seed pods and probably also of deliberate introduction as a fodder plant; the relative importance of these two means of spread cannot be determined. The species can be a useful pasture plant, in particular because of its nitrogen-fixing ability, but in other places it is considered to be an invasive weed; it can sometimes be toxic to livestock, and the seed pods can be a serious contaminant of wool.
Taxonomic TreeTop of page
- Domain: Eukaryota
- Kingdom: Plantae
- Phylum: Spermatophyta
- Subphylum: Angiospermae
- Class: Dicotyledonae
- Order: Fabales
- Family: Fabaceae
- Subfamily: Faboideae
- Genus: Medicago
- Species: Medicago polymorpha
Notes on Taxonomy and NomenclatureTop of page
M. polymorpha has been given several different botanical names over the years, M. denticulata Willd. and M. hispida Gaertn. being two of the more common. In a few countries like New Zealand the preferred name is M. nigra (L.), following the treatment by Lesins and Lesins (1979), quoted in Webb et al. (1998). Many different cultivars have been named: plant breeders show most interest in Medicago polymorpha var. brevispina, distinguished by the lack of hooked spines on the burs. This means it is much less likely to become entangled in and downgrade wool.
DescriptionTop of page
The following description is from eFloras (2013):
‘Annual or biennial herbs, 20-90 cm. Stems prostrate or ascending, branched at base, subquadrangular, glabrescent. Stipules ovate-oblong, 4-7 mm, base auriculate, margin irregularly laciniate or deeply incised, apex acuminate; petioles long and thin, 1-5 cm; leaflets obovate or triangular-obovate, 7-20 × 5-15 mm, papery, sparsely hairy abaxially, glabrous adaxially, base broadly cuneate, margin shallowly serrate in apical 1/3, apex obtuse, truncate, or emarginate, apiculate. Flowers (1 or) 2-10 in axillary racemes; peduncles slender, 3-15 mm, usually longer than leaves; pedicel less than 1 mm. Corolla yellow, 3-4 mm; standard obovate, emarginate. Legume ash-green to greenish brown, discoid, 4-6(-10) mm, tightly coiled in 1.5-2.5(-6) spirals, turning clockwise, radial veins connected near edge on coil face, spines or tubercles 15 in each row. Seed brown, reniform, ca. 2.5 × 1.25 mm, smooth.’
Distribution TableTop of page
The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.
|Continent/Country/Region||Distribution||Last Reported||Origin||First Reported||Invasive||Reference||Notes|
|China||Present||Present based on regional distribution.|
|-Hong Kong||Present||Introduced||PIER, 2013|
|East Timor||Present||Introduced||Council of Heads of Australasian Herbaria, 2013|
|Georgia (Republic of)||Present||Native||USDA-ARS, 2013|
|Saudi Arabia||Present||Native||USDA-ARS, 2013|
|Turkey||Present||Native||Cimalová, 2012; USDA-ARS, 2013|
|United Arab Emirates||Present||Native||USDA-ARS, 2013|
|Ethiopia||Present||Mengistu, 1987||Quite frequent above 1700m|
|South Africa||Present||Introduced||USDA-ARS, 2013|
|-Canary Islands||Present||Native||USDA-ARS, 2013|
|Canada||Present||Present based on regional distribution.|
|-British Columbia||Present||Introduced||USDA-ARS, 2013|
|-New Brunswick||Present||Introduced||USDA-ARS, 2013|
|USA||Present||Present based on regional distribution.|
|-Hawaii||Present||Introduced||Invasive||PIER, 2013; USDA-NRCS, 2013||Cultivated and invasive|
|-Missouri||Present, few occurrences||Introduced||USDA-NRCS, 2013|
|-New Jersey||Present||Introduced||USDA-NRCS, 2013|
|-New Mexico||Present||Introduced||USDA-NRCS, 2013|
|-New York||Present||Introduced||USDA-NRCS, 2013|
|-North Carolina||Present||Introduced||USDA-NRCS, 2013|
|-Rhode Island||Present||Introduced||USDA-NRCS, 2013|
|-South Carolina||Present||Introduced||USDA-NRCS, 2013|
Central America and Caribbean
|Costa Rica||Present||Introduced||USDA-ARS, 2013|
|Belgium||Present||Introduced||USDA-ARS, 2013||Possibly introduced|
|Czech Republic||Present, few occurrences||Introduced||Cimalová, 2012|
|Czechoslovakia (former)||Present||Introduced||USDA-ARS, 2013||Possibly introduced|
|Denmark||Present||Introduced||Not invasive||NOBANIS, 2013||Rare|
|Hungary||Present||Introduced||USDA-ARS, 2013||Possibly introduced|
|Netherlands||Present||Introduced||USDA-ARS, 2013||Possibly introduced|
|-Azores||Present||Introduced||USDA-ARS, 2013||Possibly introduced|
|Russian Federation||Present||Native||USDA-ARS, 2013|
|-Southern Russia||Present||Native||Australian Weeds Committtee, 2013|
|Sweden||Present||Introduced||Not invasive||NOBANIS, 2013||Rare|
|Switzerland||Present||Introduced||USDA-ARS, 2013||Possibly introduced|
|UK||Present||Introduced||Clapham et al., 1962||Localised in coastal Eastern and Southern areas|
|Yugoslavia (former)||Present||Native||USDA-ARS, 2013|
|Australia||Present||Introduced||Invasive||Australian Weeds Committtee, 2013|
|-Australian Northern Territory||Present||Introduced||Invasive||Council of Heads of Australasian Herbaria, 2013|
|-Lord Howe Is.||Present||Introduced||Invasive||PIER, 2013|
|-New South Wales||Widespread||Introduced||Invasive||Australian Weeds Committtee, 2013|
|-Queensland||Localised||Introduced||Invasive||Australian Weeds Committtee, 2013||Southern and Central Queensland|
|-South Australia||Widespread||Introduced||Invasive||Australian Weeds Committtee, 2013|
|-Tasmania||Widespread||Introduced||Invasive||Australian Weeds Committtee, 2013|
|-Victoria||Widespread||Introduced||Invasive||Australian Weeds Committtee, 2013|
|-Western Australia||Localised||Introduced||Invasive||Australian Weeds Committtee, 2013||Southern Western Australia|
|New Caledonia||Present||Introduced||Invasive||PIER, 2013|
|New Zealand||Widespread||Introduced||Invasive||Webb et al., 1988||Known as M. nigra|
|Norfolk Island||Present||Introduced||PIER, 2013|
|US Minor Outlying Islands||Present||Introduced||Invasive||PIER, 2013||Midway Atoll|
History of Introduction and SpreadTop of page
Viable M. polymorpha seeds were extracted from adobe bricks from eighteenth-century buildings in San Vincente, Mexico (Spira and Wagner, 1983), and the species may have been introduced to Chile as much as 450 years ago (Pozo et al., 1989, quoted in Paredes et al., 2002). Introduction to countries like Australia, New Zealand and South Africa probably occurred during the spread of British emigrants in the nineteenth century, when settlers often took with them such possessions as vegetation-stuffed mattresses, hay and straw for livestock, vegetation as packaging material, and grass and other plant seed for cultivation in the new country.
IntroductionsTop of page
|Introduced to||Introduced from||Year||Reason||Introduced by||Established in wild through||References||Notes|
|Natural reproduction||Continuous restocking|
|Australia||Europe||1848||Hitchhiker (pathway cause)||Yes||CHAH (2014); Council of Heads of Australasian Herbaria (2013)||First found near Adelaide; probably introduced from Europe|
|Chile||Europe||1500s||Hitchhiker (pathway cause)||Yes||Pozo et al. (1989)||Probably introduced from Europe|
|Mexico||Europe||1790||Hitchhiker (pathway cause)||Yes||Spira and Wagner (1983)||Probably introduced from Europe|
|New Zealand||Europe||1855||Hitchhiker (pathway cause)||Yes||Hooker (1867)||In Auckland province; probably introduced from Europe|
Risk of IntroductionTop of page
Intentional introduction as a pasture plant is still likely, especially of new and improved cultivars. Accidental introduction is less likely than it used to be, as M. polymorpha seed ought to be detected in phytosanitary searches of samples of crop or pasture seed crossing international boundaries, but it is still possible. The species is already fairly widely distributed.
HabitatTop of page
Where M. polymorpha has been introduced, as in California, it occurs in a wide variety of ‘disturbed’ sites, including lawns and turf, roadsides, fields, grasslands, pastures, agricultural sites (UC IPM, 2013); Parker and Gilbert (2007) noted that it was invasive and one of the commonest legumes in coastal Californian prairies. In Hawaii it is 'naturalized in open, dry to occasionally mesic, disturbed areas such as pastures, roadsides and vacant lots, 0-1220 m [altitude?]' (Wagner et al., 1999, cited in PIER, 2013). In Australia it is found in a wide variety of vegetation communities ranging from open grasslands to shrublands and woodlands, and grows on a wide range of soils, but does best in alkaline soils, growing most prolifically on heavy clays (Department of Primary Industries, Victoria, 2013). In Chile it is distributed over a remarkable range of bioclimatic and soil conditions throughout the Mediterranean-climate region of the country (Pozo et al., 1989, quoted in Paredes et al., 2002).
Around its native Mediterranean, the website Flowers in Israel (Modzelevich, 2013) describes its habitat as ‘woodlands and shrublands, semi-steppe shrublands, shrub-steppes, deserts and extreme deserts, montane vegetation of Mt. Hermon.’
In Britain, the Online Atlas of the British and Irish Flora (Biological Records Centre, 2013) reports that the species is ‘found in open sandy and gravelly habitats by the coast. It occurs in short, open grassland on summer-parched banks and cliffs with other annuals, particularly in S.W. England. Inland, like other Medicago species, it occurs as a casual, especially with wool shoddy.’ The same source says that the species ‘has declined at its coastal stations through scrub encroachment and lack of grazing, although it may be overlooked or confused with M. arabica. It is much scarcer nowadays as a casual inland’. The spiny pods stick to wool and other fibres, which helps their dispersal and explains its association in Britain with wool shoddy (recycled wool).
In Syria, Ehrman and Cocks (1990) found that M. polymorpha occurred on almost all soil types, and was found in almost every climatic zone in that country.
Habitat ListTop of page
|Terrestrial – Managed||Cultivated / agricultural land||Principal habitat||Natural|
|Managed forests, plantations and orchards||Present, no further details||Natural|
|Managed grasslands (grazing systems)||Principal habitat||Natural|
|Disturbed areas||Principal habitat||Natural|
|Rail / roadsides||Present, no further details||Natural|
|Terrestrial ‑ Natural / Semi-natural||Natural forests||Present, no further details||Natural|
|Natural grasslands||Present, no further details||Natural|
|Scrub / shrublands||Present, no further details||Natural|
|Deserts||Present, no further details||Natural|
|Arid regions||Present, no further details||Natural|
Biology and EcologyTop of page
2n=14. As its botanical name indicates, M. polymorpha displays a wide range of phenotypic characters, which often relate to ecological factors. Studies of phenotypic and genetic variability have been carried out in Chile (Pozo et al., 2002a, b; Paredes et al., 2002), Tunisia (Hannachi et al., 1998), Sardinia (Bullitta et al., 1994) and elsewhere, often in the search for improved cultivars for agricultural use. Although there seems to be appreciable variation in the genotypes of the species in Tunisia, this is not so in Chile, one reason for which may be, as Paredes et al. (2002) speculate, that only a small number of individuals were originally introduced into Chile.
M. polymorpha is an annual or sometimes a biennial plant, reproducing entirely by seed. Depending on the climatic zone in which plants originate, they can be obligatory or facultative long-day plants (Pozo et al., 2000). Accessions from wetter areas (mean annual rainfall over 1200 mm) did not flower under continuous 8-hour photoperiods for the 111-day (4-month) duration of one experiment, whereas most accessions from arid to sub-humid areas flowered even under 8-hour photoperiods: all accessions flowered earlier (in as little as 24 days in one case) with exposure to longer photoperiods. This means that plants from drier areas of Chile, where frosts are less likely, flower earlier than those from wetter areas, where the chance of frosts is greater (Pozo et al., 2000).
The flowers are followed by indehiscent coiled pods (burrs) which are often covered in hooked spines which make the pods stick to animal fibres or clothing. The pods never open and as some seeds germinate, others remain dormant within the pod (Wagner and Spira, 1994). Jain (1982) found a high level of dormancy in seeds tested in July after collection in June: by September the mean percentage of germinating seeds from 13 populations had risen from 8.4 % to 16.1 %. This hard-seededness or dormancy is a characteristic of some leguminous species of clovers and medics. Some seeds of M. polymorpha can remain dormant for several years, with release from dormancy brought about by long exposure to temperature and moisture fluctuations (Wagner and Spira, 1994).
In California (and presumably in similar Mediterranean climates) germination usually occurs following the first significant autumn rains, between September and December in the Northern Hemisphere (Wagner and Spira, 1994). In early November, following mid-October rains, the same authors analysed sod samples and found that 40.3% of all seeds recovered were dormant, 6.3 % germinated and died, and 53.4 % became established seedlings. Although seedling mortality was high in both wet and dry winters, in an unusually dry year only about 10 % of seedlings survived to fruiting, and plants were small and produced few fruits. In an unusually wet year, by contrast, about 50% of seedlings survived to produce fruits (Wagner and Spira, 1994).
Physiology and Phenology
Frost tolerance in different ecotypes of M. polymorpha is related to the geographical origin of those ecotypes in both Syria (Cocks and Ehrman, 1987) and Chile (Pozo et al., 2002a). Pozo et al. (2002b) found greater winter vigour in plants originally collected from drier, warmer, less frosty northern regions of Chile than in those from humid southern regions, when they were grown together in the intermediate ‘Mediterranean’ climate zone.
Although the plants of M. polymorpha themselves are short lived, 200 year-old viable seeds have been found on the surface of adobe bricks in Northern Mexico (Spira and Wagner, 1983). As these authors point out, the longevity of these seeds may have been favoured by the dry stable environment of adobe bricks, and reduced temperature fluctuation and microbial activity may also have played a part.
M. polymorpha forms a symbiotic relationship with the bacteria Ensifer medicae (= Sinorhizobium medicae) or E. meliloti (= S. meliloti), which invade plant roots and form root nodules. In these the bacteria gain nutrition from the plant and fix atmospheric nitrogen to help sustain the plant. The amount of nitrogen fixed can be substantial (about 25 kg per tonne of legume dry matter) according to Peoples and Baldock (2001) in a study of Australian pasture legumes in general.
M. polymorpha occupies a very wide range of habitats and climatic zones and therefore associates with many other species of plants, some of which often have a similar Mediterranean origin.
M. polymorpha is widely distributed around the Mediterranean and tolerates a wide variety of habitats. It is well adapted to neutral and slightly acid soils, to altitudes of 10 to 900 m or more, and to annual rainfall from 100 to 800 mm. (Hannachi et al., 1998). The species is also widespread where it has been introduced to other countries with similar climates – Australia, Chile, South Africa and the United States. As Graziano et al. (2010) say ‘it is now found over a remarkable range of bioclimatic and soil conditions’.
ClimateTop of page
|Cs - Warm temperate climate with dry summer||Preferred||Warm average temp. > 10°C, Cold average temp. > 0°C, dry summers|
Air TemperatureTop of page
|Parameter||Lower limit||Upper limit|
|Mean annual temperature (ºC)||10.5||27.5|
RainfallTop of page
|Parameter||Lower limit||Upper limit||Description|
|Mean annual rainfall||100||1000||mm; lower/upper limits|
Natural enemiesTop of page
|Natural enemy||Type||Life stages||Specificity||References||Biological control in||Biological control on|
Notes on Natural EnemiesTop of page
Major pests of M. polymorpha in Australia listed by Howie et al. (2007) are: redlegged earth mite (Halotydeusdestructor), lucerne flea (Sminthurus viridis), bluegreen aphid (Acyrthosiphon kondoi), cowpea aphid (Aphis craccivora), spotted alfalfa aphid (Therioaphis trifolii), sitona weevil (Sitonadiscoideus) and the root lesion nematode Pratylenchus neglectus. Major diseases are phoma black-stem (Phoma medicaginis), rhizoctonia bare-patch (Rhizoctonia solani[Thanatephorus cucumeris]) and powdery mildew (Erysiphe trifolii). Uromyces ciceris-arietini (chickpea rust) (Stuteville et al., 2013), U. pisi-sativi (Storey, 2013), and U. anthyllidis (Landcare Research, 2013) have also been recorded as infesting M. polymorpha.
Means of Movement and DispersalTop of page
Natural Dispersal (Non-Biotic)
The non-dehiscent fruits are relatively large and are unlikely to move far from the parent plant, except perhaps in flood waters.
Vector Transmission (Biotic)
Green et al. (2008) found an apparently intact seed of M. polymorpha in the faeces of a black swan (Cygnus atratus). Seeds have also been found in cattle dung in Argentina (Vignolio and Fernández, 2010); they easily survive passage through horses (St John-Sweeting and Morris, 1990), and some pass unharmed through the guts of sheep, both in South Africa (Kotzéac et al., 1995) and in Australia (Edward et al., 1998).
The hooked spines commonly, but not always, found on the fruits allow the entire burrs to adhere firmly to the wool of sheep or the hair of horses, American bison (Bison bison L.) (Constible et al., 2005) and other animals, and to the hair and clothes of humans. Their occurrence in sheep’s wool in Australia is described by the Australian Wool Testing Authority (2002) as follows: ‘Burr Medic is very common in Australian wools and is one of the most troublesome types to processors. Not only do its protruding spines catch in the wool, making them difficult to remove, but also, if broken up during carding, its coils tend to unwind into thin ‘eyebrow’ shaped pieces which are even more difficult to remove and can persist into the finished product’.
With modern seed cleaning and inspection services, further accidental introduction of M. polymorpha is less likely than it used to be (although still possible), but the species is already widely distributed throughout much of the world, having probably been spread in hay and straw transported for livestock, in vegetation used as packaging and in plant seed transported for cultivation.
Intentional introduction to countries where grazed grasslands are important is likely to continue, since many countries are searching for improved cultivars to improve the productivity of their pastures.
Plant TradeTop of page
|Plant parts liable to carry the pest in trade/transport||Pest stages||Borne internally||Borne externally||Visibility of pest or symptoms|
|True seeds (inc. grain)||seeds||Yes||Pest or symptoms usually visible to the naked eye|
Impact SummaryTop of page
|Economic/livelihood||Positive and negative|
Economic ImpactTop of page
As mentioned in the 'Means of Movement and Dispersal' section, the burrs of M. polymorpha cause serious degradation of the Australian wool clip and reduce its value – they are difficult to remove, and if they are broken up during carding, their coils tend to unwind into thin ‘eyebrow’ shaped pieces which are even more difficult to remove and can persist into the finished product (Australian Wool Testing Authority, 2002).
At the same time in Australia and elsewhere – Chile (Pozo et al., 2002a,b), Sicily (Graziano et al., 2010), Tunisia (Hannachi et al., 1998), Syria (Ehrman and Cocks, 1990) – the species is seen as a valuable self-sustaining, nitrogen-fixing addition to pastures for grazing animals, and the search for better cultivars is continuing. In Australia at least three cultivars (Circle Valley, Serena and Santiago) have been commercially produced (Hannachi et al., 1998). However these cultivars have shown poor adaptability to real Mediterranean environments (Graziano et al., 2010). Chile has also produced its own cultivar of M. polymorpha suitable for the arid, semiarid and subhumid Mediterranean zones of Chile (Pozo et al., 2001).
In an article on the Russian Steppe, Boonman and Mikhalev (2005) say: ‘Although it is well eaten, M. polymorpha can be a most harmful plant because the pods spoil the wool. It can be suppressed by hard and prolonged grazing. Herbicides are also effective.’
In Egypt, M. polymorpha apparently ‘causes great damage to flax production’ (Hozayn et al., 2010).
According to Howie et al. (2007)M. polymorpha can cause photosensitisation in horses, occasionally red gut in sheep, and bloat in cattle. Phytoestrogens/coumestrols can potentially have negative effects on the reproduction of grazing livestock but this is rarely reported (levels tend to be higher under conditions of phosphorus deficiency and Phoma infection).
Environmental ImpactTop of page
Many countries with Mediterranean climates, like Chile, Australia and those around the Mediterranean, see M. polymorpha as a valuable grassland component, both providing fodder for livestock and enhancing the supply of nitrogen for grass growth. Parts of the USA (California, Arizona, Nevada), however, regard the species as an invasive species or weed, although in other parts of the USA (the Upper Midwest) Australian cultivars have been evaluated as a possible ‘valuable addition to agricultural systems’ (Haan et al., 2002).
Cal-IPC (2013) has evaluated M. polymorpha for its ‘level of threat to the ecological health of wildlands through evaluation of its ecological impact, ability to invade natural vegetation communities, and current extent of its invasion.’ These criteria were developed for use in California, Arizona, and Nevada and the outcome of the evaluation describes the ‘ecological amplitude’ of the species as ‘Limited’, meaning that it invades only one major ecological type and two to four minor types.
The points that this evaluation raises are:
- Greater fire intensity may result from increased grass biomass caused by its nitrogen fixation,
- Herbivore populations may be increased by its better nutritional value,
- It has probably spread to most locations where it can survive,
- It does not thrive well outside grazed grasslands,
- It can recover from grazing if this is not too severe,
- Human-caused dispersal is not expected to be frequent, although seeds can be dispersed as commercial seed contaminants.
- When livestock are moved any attached seed pods can be moved with them,
- High levels of infestation (in grasslands) are not generally found unless the site is fertilized and moderately grazed.
Social ImpactTop of page
M. polymorpha probably has very little direct social impact.
Risk and Impact FactorsTop of page Invasiveness
- Proved invasive outside its native range
- Has a broad native range
- Abundant in its native range
- Pioneering in disturbed areas
- Fast growing
- Has high reproductive potential
- Has propagules that can remain viable for more than one year
- Ecosystem change/ habitat alteration
- Modification of fire regime
- Modification of nutrient regime
- Negatively impacts animal health
- Damages animal/plant products
- Produces spines, thorns or burrs
- Highly likely to be transported internationally deliberately
UsesTop of page
The development of improved cultivars of M. polymorpha for oversowing in grazed pasture in Australia and their testing in other countries including the USA and Sicily, as well as the search for improved local cultivars in Syria, Tunisia, Chile and elsewhere (Pozo et al., 2002a, b; Graziano et al., 2010; Hannachi et al., 1998; Ehrman and Cocks, 1990), indicate that in many places it is sought after as a useful addition to grazed pastures, particularly because of its nitrogen-fixing ability.
Indirect social benefits could arise from the use of improved grazing land in several countries.
M. polymorpha has the potential to increase the availability of nitrogen to pastoral systems, an effect which can be considered positively by graziers or negatively by environmentalists.
Similarities to Other Species/ConditionsTop of page
M. polymorpha is very similar to and often grows with M. arabica (sometimes known as M. polymorpha var. arabica), but differs in NOT having dark spots or markings on the upper surface of each leaflet – instead it has reticulately veined pods and more or less erect spines.
Small and Jomphe (1989) point out that ‘M. polymorpha is the most common ruderal Medicago (except possibly for escaped alfalfa, M. sativa), the most likely to be collected, and the most likely to be confused with other species’.
Prevention and ControlTop of page
Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.
According to Florabase (Western Australian Herbarium, 2013), M. polymorpha in the Swan River area of Western Australia is relatively tolerant to glyphosate, grazing and mowing. They suggest hand pulling isolated plants in winter before flowering, or the use of herbicides (see below).
Biological control of M. polymorpha has never been considered because the species is seen as a useful component of pastures in several parts of the world. However, a number of insects, nematodes and fungi are known to attack it (see the ‘Notes on Natural Enemies’ section for more details).
It is suggested in Florabase (Western Australian Herbarium, 2013) that as M. polymorpha in the Swan River area of Western Australia is relatively tolerant to glyphosate, instead clopyralid, metsulfuron or triasulfuron can be used as herbicides to give reasonably selective control, but their use must be repeated annually for several years. In California, isoxaben is suggested for the control of clovers in general (Smith et al., 2013). Boonman and Mikhalev (2005) indicate that herbicides are effective in the Russian steppes.
Control by Grazing
Heavy grazing will certainly reduce the incidence of M. polymorpha in pastures, but not for long, as recovery from buried seed will occur at the next rains; Boonman and Mikhalev (2005) state that ‘hard and prolonged’ grazing can suppress it.
ReferencesTop of page
Australian Weeds Committtee, 2013. Weeds of Australia. Canberra, Australia: Australian Weeds Committtee. http://www.weeds.org.au/
Australian Wool Testing Authority, 2002. Testing the Wool Clip. Kensington, Victoria, Australia: Australian Wool Testing Authority, 26 pp. http://www.awtawooltesting.com.au/index.php/en/component/edocman/?task=document.download&id=35
Biological Records Centre, 2013. Online Atlas of the British and Irish flora. Wallingford, UK: Biological Records Centre. http://www.brc.ac.uk/plantatlas/
Boonman JG; Mikhalev SS, 2005. The Russian Steppe. In: Grasslands of the World [ed. by Suttie, J. M. \Reynolds, S. G. \Batello, C.]. Rome, Italy: Food and Agriculture Organization of the United Nations, 381-416. [Plant Production and Protection Series no. 34.] ftp://ftp.fao.org/docrep/fao/008/y8344e/y8344e10.pdf
Bullitta S; Floris R; Hayward MD; Loi A; Porqueddu C; Veronesi F, 1994. Morphological and biochemical variation in Sardinian populations of Medicago polymorpha L. suitable for rainfed Mediterranean conditions. Euphytica, 77(3):263-268.
Cal-IPC (California Invasive Plant Council), 2005. Cal-IPC Plant Assessment Form for Medicago polymorpha. Berkeley, California, USA: California Invasive Plant Council. http://www.cal-ipc.org/paf/site/paf/380
Cocks PS; Ehrman TAM, 1987. The geographic origin of frost tolerance in Syrian pasture legumes. Journal of Applied Ecology, 24:673-683.
Constible JM; Sweitzer RA; Vuren DH van; Schuyler PT; Knapp DA, 2005. Dispersal of non-native plants by introduced bison in an island ecosystem. Biological Invasions, 7(4):699-709. http://www.springerlink.com/media/99eqac4jng3tnn4c1v5q/contributions/n/v/7/4/nv745xl0n172j707.pdf
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ContributorsTop of page
13/03/13: Original text by:
Ian Popay, consultant, New Zealand, with the support of Landcare Research.
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