Senecio inaequidens (South African ragwort)
- Summary of Invasiveness
- Taxonomic Tree
- Notes on Taxonomy and Nomenclature
- Plant Type
- Distribution Table
- History of Introduction and Spread
- Risk of Introduction
- Habitat List
- Hosts/Species Affected
- Host Plants and Other Plants Affected
- Biology and Ecology
- Air Temperature
- Rainfall Regime
- Soil Tolerances
- Natural enemies
- Notes on Natural Enemies
- Means of Movement and Dispersal
- Pathway Causes
- Pathway Vectors
- Impact Summary
- Economic Impact
- Environmental Impact
- Social Impact
- Risk and Impact Factors
- Similarities to Other Species/Conditions
- Prevention and Control
- Gaps in Knowledge/Research Needs
- Distribution Maps
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PicturesTop of page
IdentityTop of page
Preferred Scientific Name
- Senecio inaequidens DC.
Preferred Common Name
- South African ragwort
Other Scientific Names
- Senecio burchellii DC.
International Common Names
- English: narrow-leaved ragwort
- French: séneçon du Cap
Local Common Names
- Germany: Schmalblättriges Greiskraut; Schmalblättriges Kreuzkraut; Südafrikankisches Greiskraut
- Italy: senecione sudafricano
- SENIQ (Senecio inaequidens)
Summary of InvasivenessTop of page
S. inaequidens is a herbaceous perennial considered native to South Africa. It has spread rapidly in North and Central Europe following its accidental introduction from South Africa in wool exports. In the absence of rigorous phytosanitary controls, it is very likely to spread further along roads and railways. As its present realized niche differs to a large extent from its equilibrium niche (Vacchiano et al., 2013), it has to be expected that the species will spread into grasslands and pastures in the near future. S. inaequidens is a prolific achene producer, has vigorous growth and is toxic. Its economic impacts are currently minimal, and so far, no environmental impacts have been observed; however, due to its toxicity, its potential to spread into arable land should be considered a serious threat for cattle and human health. This species should in no case be considered for cultivation, even though its usefulness for health care (for example) has been demonstrated.
Taxonomic TreeTop of page
- Domain: Eukaryota
- Kingdom: Plantae
- Phylum: Spermatophyta
- Subphylum: Angiospermae
- Class: Dicotyledonae
- Order: Asterales
- Family: Asteraceae
- Genus: Senecio
- Species: Senecio inaequidens
Notes on Taxonomy and NomenclatureTop of page
The morphological variation within S. inaequidens has led to a complex and confusing taxonomy for the species, particularly for the identity of the introduced taxon. This is due to the superficial similarity between two disjunct groups of species, one in South Africa and Madagascar (S. madagascariensis Poiret complex; Hilliard, 1977) and the other in Australia (S. lautus Forster f. ex Willd. complex; Ali, 1969). S. inaequidens belongs to the latter complex.
The initial point of confusion appears in de Candolle's original description of S. burchellii DC.; two of the specimens cited are indistinguishable from the type of S. inaequidens (Hilliard and Burtt, 1975), although one specimen matches the description of S. burchellii. S. burchellii can be separated from S. inaequidens by the turbinate capitulum, few involucral bracts (ca. 12 versus ca. 20) and few ray florets (ca. 7 versus ca. 12) and is found in the south-western and western Cape. The weed that is commonly called 'S. burchellii' in eastern South Africa is S. inaequidens.
S. reclinatus is a synonym of S. paniculatus (Harvey, 1865), a species which can be separated from S. inaequidens by its many, slender involucral bracts. S. douglasii is a North American species, commonly called thread-leaved ragwort. S. vimineus Harvey non DC., is a synonym of S. harveianus MacOwan, which can be distinguished from S. inaequidens by its larger involucral bracts ((5-)6-7(-9) mm versus (4-)5(-7) mm) and its extensive calyculus of three to four series of dark-tipped, overlapping bracts (Hilliard, 1977). However, S. harveianus, as used by Jovet and Bosserdet (1962), is S. inaequidens.
The Latin epithet 'inaequidens' means unequal teeth and presumably refers to the variation in leaf margin dentition that may be found even in a single plant. The English common names refer to the presumed origin of the species in South Africa or its narrow leaves.
The distinction between S. inaequidens and S. madagascariensis is controversial. Traditionally a distinction has been made between these two taxa, whilst recent evidence suggests that they are conspecific, differing only in ploidy level (Scott et al., 1998; see also López et al., 2008).
In databases and online, the 'ae' diphthong in 'inaequidens' may be, incorrectly, transcribed as either 'inequidens' or 'inaquidens'.
DescriptionTop of page Herbaceous, woody (at base) short-lived perennial, up to 100 cm tall, arising from a shallow taproot. Stems are erect, ±glabrous, often much branched from the base. Leaves alternate, bright green, usually clasping stem at the base (occasionally petiolate), becoming reduced in size from the base, very variable, up to 10 cm long and 1 cm wide (usually much narrower). Cauline leaves mostly linear-lanceolate to elliptic-lanceolate, apex acute, margins denticulate to coarsely and irregularly toothed (occasionally pinnately lobed), tapering to a narrow petiole-like amplexicaule base, sometimes auriculate. Upper leaves occasionally pinnately lobed, shortly petiolate, subsessile or sessile. Leaves differ in the degree of dissection and width of the lobes. Inflorescence an open, terminal or axillary, corymbose panicle. Capitula up to 25 mm diameter, radiate, involucral bracts lanceolate (ca. 20), acute, ±glabrous, keeled, (4-)5(-7) mm long, resinous; calyculus bracts few, acute, ±glabrous, dark-tipped. Ray florets (7-)13, female, ligule bright yellow, becoming revolute. Disc florets numerous, perfect, tube bright yellow, lobes with a median resinous line. Achenes 2-2.5 mm long, cylindrical, pubescent between ribs. Pappus white, 2- to 3-times as long as achenes, readily detached. Description based on Hilliard (1977).
Plant TypeTop of page Broadleaved
DistributionTop of page
S. inaequidens is considered native to South Africa, although it is unclear whether it is native in its wider southern African distribution. S. inaequidens has invaded large areas in Europe and is also reported from Asia and Africa. Some authors treat invasive populations of S. madagascariensis reported from Australia as belonging to S. inaequidens (Lafuma et al., 2003; Monty et al., 2010). There is a report of S. inaequidens from Colombia (Najar et al., 2001), although this may refer to S. madagascariensis.
The taxonomic confusion that surrounds the identification of S. inaequidens may have led to under-recording, for example, counts of n = 20 for Argentinean S. madagascariensis (Hunziker et al., 1989) may refer to S. inaequidens. Alternatively, S. inaequidens may have been over-recorded through confusion with other species, such as S. harveianus and S. madagascariensis (Clement et al., 1994).
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|
|Taiwan||Present, few occurrences||EPPO, 2014|
|Botswana||Present||Native||Hilliard, 1977; Werner et al., 1991; EPPO, 2014|
|Lesotho||Present||Native||Werner et al., 1991; EPPO, 2014|
|Mozambique||Present||Native||Werner et al., 1991; EPPO, 2014|
|Namibia||Present||Native||Hilliard, 1977; Werner et al., 1991; EPPO, 2014|
|South Africa||Widespread||Native||Not invasive||Hilliard, 1977; EPPO, 2014|
|Swaziland||Present||Native||USDA-ARS, 2003; EPPO, 2014|
|Colombia||Absent, unreliable record||Introduced||Najar et al., 2001; EPPO, 2014|
|Andorra||Present||Introduced||Not invasive||Montserrat Recoder & Benito Alonso, 2000; EPPO, 2014|
|Austria||Present||Schinninger et al., 2002|
|Belgium||Present||Introduced||1922||Invasive||Mosseray, 1936; D'Hose and de Langhe, 1989; EPPO, 2014|
|Bulgaria||Present, few occurrences||EPPO, 2014|
|Croatia||Present||Milovic and Pandza, 2014|
|Czech Republic||Restricted distribution||Introduced||Not invasive||Pysek et al., 2002; EPPO, 2014|
|Denmark||Present||Introduced||Not invasive||Skovgaard, 1993; EPPO, 2014|
|Finland||Present, few occurrences||Introduced||Not invasive||Bornkamm, 2002; EPPO, 2014|
|France||Restricted distribution||Introduced||1935||Invasive||Jovet and Bosserdet, 1962; Chater and Walters, 1976; EPPO, 2014|
|-Corsica||Present, few occurrences||EPPO, 2014|
|Germany||Widespread||Introduced||1889||Invasive||Kuhbier, 1977; Stieglitz, 1977; Brennenstuhl, 1995; Kuhbier, 1996; EPPO, 2014|
|Italy||Widespread||Introduced||1947||Invasive||Pignatti, 1982; Martini and Zappa, 1993; Tammaro and Giglio, 1994; Brandes and, 1999; EPPO, 2014|
|Netherlands||Widespread||Introduced||1939||Invasive||NPPO of the Netherlands, 2013; Adema and Mennema, 1978; Ernst and, 1998; EPPO, 2014|
|Norway||Present, few occurrences||Introduced||Not invasive||Often, 1997; EPPO, 2014|
|Poland||Present||Introduced||Not invasive||Ernst and, 1998; EPPO, 2014; Kocián, 2016|
|Romania||Present, few occurrences||Introduced||Not invasive||Sirbu and Oprea, 2010|
|Slovenia||Restricted distribution||Introduced||Glasnovic and Pecnikar, 2010|
|Spain||Present||Introduced||Not invasive||Guillerm et al., 1990; EPPO, 2014|
|Sweden||Present||Introduced||Not invasive||Bornkamm, 2002; EPPO, 2014|
|Switzerland||Present||Introduced||Mayor, 1996; EPPO, 2014|
|UK||Present||Introduced||1908||Not invasive||Hayward and Druce, 1919; Lousley, 1961; MacPherson, 1997; EPPO, 2014|
|-England and Wales||Present||EPPO, 2014|
|-Northern Ireland||Present||EPPO, 2014|
|Australia||Present||Introduced||Monty et al., 2010|
History of Introduction and SpreadTop of page
All introductions of S. inaequidens outside of the native range appear to have been accidental. The first occurrences in Europe were around wool-processing factories in Germany (Hanover in 1889 and Bremen in 1896; Kuhbier, 1977). All the five primary sites of introduction are associated with the wool trade: Mazamet (southern France; Senay, 1944; Leredde, 1945; Guillerm et al., 1990); Calais (northern France; Antoine and Weill, 1966; Jovet and Bosserdet, 1962); Verona (northern Italy; Kiem, 1975, 1976); Lüttich (eastern Belgium; Mosseray, 1936; Lambinon, 1957; Duvigneaud, 1976) and Bremen (northern Germany; Kuhbier, 1977; Hülbusch and Kuhbier, 1979). Additional sites of introduction are also associated with the wool industry, such as Edinburgh in 1928 (Scotland, UK; Lousley, 1961) and Galashiels in 1908 (also in Scotland; Hayward and Druce, 1919; incorrectly identified as S. lautus). Initial records in the UK show the appearance of the species as an adventive. In recent years there has been an increasing number of records across Europe and the species continues to spread (Ernst, 1998). This has been most extensively documented in Germany (Werner et al., 1991; Kuhbier, 1996), the Netherlands (Ernst, 1998) and Italy (Vacchiano et al., 2013). The most important sites of initial colonization are roadsides and railways (Griese, 1996; Radkowitsch, 1997; Bornkamm, 2002); Ernst (1998) and Vacciano et al. (2013)have investigated in detail the process of colonization and spread.
Recent population genetic evidence confirms that there have been several introductions of S. inaequidens into Europe, with subsequent spread of the species along invasion routes (Lachmuth et al., 2010). Bossdorf et al. (2008) found introduced populations in Europe to be phenotypically most similar to native populations from mountainous regions in Southern Africa. The authors suggested that invasion of S. inaequidens in Central Europe is due to selective introduction of pre-adapted genotypes.
Molecular genetic studies revealed that in Morocco and the Canary Islands, S. massaicus contains genetic material of a southern African lineage which includes S. inaequidens. The authors suggest that the recent invasion of S. inaequidens in Europe therefore represents a second arrival of this lineage into the region (Pelser et al., 2012).
Risk of IntroductionTop of page
Further introductions of S. inaequidens from its native range are unlikely, as the main pathway of historic introductions (the wool trade) is no longer as significant as it used to be. But a range expansion of adventive occurrences is highly probable, owing to the risks of accidental movement by road and rail vehicles. According to range modelling, the species' current range is still dispersal limited, at least in Italy (Vacchiano et al., 2013). It should be expected that the species will colonize pastures and grasslands in the near future. Mild winters due to climate change may enhance the spread of the species in Central Europe (Nehring et al., 2013); on the other hand, an experimental study showed that temperature rise of 3°C led to a decrease in dominance of S. inaequidens when competing with the native Plantago lanceolata (Verlinden et al., 2013). As S. inaequidens can already be found in heights up to 1600 m above sea level (Vacchiano et al., 2013), and as European occurrences seem to have descended from genotypes of mountainous regions in the native area (Bossdorf et al., 2008), its further spread in high elevations in the invaded range seems probable.
HabitatTop of page
In its native South African range (Transvaal and Natal), S. inaequidens is a grassland species of the 'highveld' (ca. 1400-2800 m) but also occurs on gravelly margins of periodically flooded streams (Hilliard, 1977). S. inaequidens is found in ruderal habitats in other parts of southern Africa, although it is unclear whether it is native or introduced in these regions (Werner et al., 1991). In its introduced European range it is opportunistic with the ability to colonize a wide range of habitats, and will grow on a wide range of substrates but prefers well-drained, disturbed soils (Werner et al., 1991). In Germany, it has been found sporadically in near-natural habitats, such as rocky outcrops and coastal dunes (Nehring et al., 2013).
Habitat ListTop of page
|Terrestrial – Managed||Cultivated / agricultural land||Present, no further details||Harmful (pest or invasive)|
|Managed forests, plantations and orchards||Present, no further details||Harmful (pest or invasive)|
|Disturbed areas||Present, no further details||Natural|
|Rail / roadsides||Present, no further details||Natural|
|Urban / peri-urban areas||Present, no further details||Natural|
Hosts/Species AffectedTop of page S. inaequidens will colonize areas of logged or storm-damaged forests (Werner et al., 1991). Furthermore, it has recently been identified as a potentially serious weed of vineyards in France and Switzerland (Michez, 1994; Mayor, 1996).
Host Plants and Other Plants AffectedTop of page
|Vitis vinifera (grapevine)||Vitaceae||Main|
Biology and EcologyTop of page
The S. inaequidens/madagascariensis species complex comprises a tetraploid (2n=(4x)=40) as well as at least two diploid cytotypes (Lafuma et al., 2003; Lafuma and Maurice, 2007). In the introduced range in Europe, however, only tetraploids seem to be present (Harland, 1955; Chichiricco et al., 1979). According to their traits as expressed in the greenhouse, the tetraploid cytotypes in the native range appear to be more competitive than the native diploids (Thebault et al., 2011). Native and invasive tetraploid cytotypes also differed in traits connected to competitive ability, suggesting selection in the invaded range leading to a competition-colonisation trade off (Thebault et al., 2011). In the introduced range in Europe, S. inaequidens is less genetically variable than in its native range in South Africa (Bossdorf et al., 2008). Central European populations show differentiation and small-scale adaptation to competitive regimes (Lachmuth et al., 2011). There is an indication of dispersal trait evolution along one of the invasion routes in Central Europe (Monty et al., 2009).
There is one report of n = 20 from an Argentinian S. madagascariensis (Hunziker et al., 1989), although this may be S. inaequidens. Harland (1954; 1955) noted that an experimentally derived, narrow-leaved, male-sterile S. vulgaris variant crossed with S. inaequidens; the outcome of the cross was not noted however. Natural hybrids in either the native or introduced ranges have not been reported. However, the taxonomic confusion that exists with S. inaequidens means that detection of natural hybridization will be difficult. Nine polymorphic microsatellite markers have been developed (Justy and Maurice, 2012), and Prentis et al. (2010) developed an expressed sequence tag (EST) collection for S. madagascariensis.
Physiology and Phenology
Six pyrrolizidine alkaloids ('PAs'; inaequidenine, integerrimine, petrophine, retrorsine, senecionine, senecivernine) have been recorded from S. inaequidens (Röder et al., 1981; Bicchi et al., 1985; Mattocks, 1986; Rizk, 1991).
The closely related species S. madagascariensis contains some PAs which are highly toxic to animals and humans (Mattocks, 1986), and it has been suggested that this is the case for S. inaequidens too (Scherber et al., 2003). PAs are not toxic to mammals per se; rather the hazard arises through the normal oxidative detoxification mechanisms in the liver that convert them to pyrrolic metabolites (dehydroalkaloids; Mattocks, 1986). Hepatotoxicity or carcinogenicity of these highly reactive electrophilic alkylating agents is a result of their binding to nucleophilic centres in tissues or to cross-link DNA (Mattocks, 1986; Woo et al., 1993; Stegelmeier et al., 1999; Fu et al., 2001).
In S. jacobaea there is considerable variation in the total PA concentration and concentration of individual PAs from plant-to-plant (Witte et al., 1992). Hartmann and Zimmer (1986) found that the highest PA content occurred in the capitula, and that PA concentration was five- to ten-fold higher than in the roots and leaves. A highly plastic process of translocation of PA precursors and allocation of PAs within the plant gives S. inaequidens a powerful defence strategy (Hartmann and Dierich, 1998).
S. inaequidens is a short-lived perennial. Capitula open when expanding disc florets force the involucral bracts apart. Disc florets open later (centripetally). In its Netherlands range, the capitula open from mid-May to mid-October, although some flowering extended into mid-November (Ernst, 1998). The capitula are visited by many types of insect, mainly Hymenoptera, Lepidoptera and Diptera (Ernst, 1998; Vanparys et al., 2008). In pollination experiments, Lopez-Garcia and Maillet (2005) showed significant reduction in the number of viable achenes (7.5%) after self-pollination in comparison with insect- and cross-pollination. This self-incompatibility is likely to be sporophytic like in other Asteraceae (Hiscock, 2000). The level of self-incompatibility varies from plant to plant, which may ensure the production of some offspring in low population sizes during colonization events (Lopez-Garcia and Maillet, 2005). Thus, S. inaequidens seems to be another example of a successful self-incompatible colonizer in the genus like S. squalidus (Brennan et al., 2002), S. madagascariensis and S. jacobaea.
Propagation is primarily by achenes, although vegetative propagation by rooting of stems that touch the ground also occurs (Ernst, 1998). Individual S. inaequidens plants vary greatly in the numbers of achenes that they produce (Ernst, 1998). Information on achene longevity is limited, although achenes may remain viable for at least 2 years when stored dry (Ernst, 1998). Achenes are able to germinate over a wide range of temperatures with an optimum at 20°C (Lopez-Garcia and Maillet, 2005).
S. inaequidens is opportunistic with the ability to colonize a wide range of habitats. It can survive under most soil moisture conditions, even hot, dry summers, and overwinters successfully in areas where temperatures reach -15° C (Ernst, 1998). Growth and development are favoured by high soil moisture (Arrieta, 2004) and high nutrient availability (Lopez-Garcia and Maillet, 2005). Diploid cytotypes present in the native range are not able to survive European winters, whereas the tetraploid cytotypes occuring in Europe are winter resistant (Monty et al., 2010). S. inaequidens prefers southern slopes (Vacchiano et al., 2013). So far, S. inaequidens occurrences are negatively associated with elevations (Vacchiano et al., 2013), but as the species can already be found in heights up to 1600 m above sea level (Vacchiano et al., 2013), and as European occurrences seem to have descended from genotypes of mountainous regions in the native area (Bossdorf et al., 2008), its further spread in high elevations in the invaded range seems probable. S. inaequidens has been found growing on Cu-contaminated soils (Bes et al., 2009) and serpentine lithosols (Martini and Zappa, 1993).
Air TemperatureTop of page
|Parameter||Lower limit||Upper limit|
|Absolute minimum temperature (ºC)||-15|
|Mean annual temperature (ºC)||10||20|
|Mean maximum temperature of hottest month (ºC)||30||35|
|Mean minimum temperature of coldest month (ºC)||-5||0|
RainfallTop of page
|Parameter||Lower limit||Upper limit||Description|
|Mean annual rainfall||500||1500||mm; lower/upper limits|
Rainfall RegimeTop of page Summer
Soil TolerancesTop of page
Special soil tolerances
Natural enemiesTop of page
|Natural enemy||Type||Life stages||Specificity||References||Biological control in||Biological control on|
|Ensina hyallipennis||Herbivore||Leaves||not specific|
|Longitarsus jacobaeae||Herbivore||Stems||not specific|
|Oryctolagus cuniculus||Herbivore||Seeds||not specific||Colombia|
|Puccinia lagenophorae||Pathogen||Leaves||to genus|
|Tyria jacobaeae||Herbivore||Leaves||not specific|
Notes on Natural EnemiesTop of page
No information is available on natural enemies of S.inaequidens in its native range. Invasive genotypes of S. inaequidens have been shown to be less palatable and to contain a higher total concentration of pyrrolizdine alkaloids than native genotypes (Cano et al., 2009); nevertheless, generalist herbivores (gastropods and rabbits) have been shown to prefer S. inaequidens over its native relative in Belgium, Jacobaea vulgaris (Jacquemart et al., 2013). Tyria jacobaeae larvae, a Lepidopteran that usually sequesters pyrrolizidine alkaloids from S. jacobaea, has been recorded from S. inaequidens in the Netherlands (Ernst, 1998). In an experiment under free-choice field conditions, though, this species did not feed on S. inaequidens (Scherber et al., 2003). In the same experiment conducted in England, the specialist beetle Longitarsus jacobaeae fed on S. inaequidens. The aphid Aphis jacobaeae can also be found feeding on S. inaequidens (Witte et al., 1990). In Colombia, the fly Ensina hyalipennis and the moth Homoeosoma oconequensis have been reported to feed on seeds of S. inaequidens (Nájar et al., 2001). Puccinia lagenophorae appears to be specific to the genus Senecio and is being tested as a mycoherbicide for common groundsel weed (S. vulgaris) in Europe (Poinso et al., 2003). Feige et al. (2002) found the microfungus Leptosphaeria derasa on S. inaequidens in Germany.
Means of Movement and DispersalTop of page
Natural Dispersal (Non-Biotic)
Achenes are wind-dispersed. In a combination of experiments and modelling, Monty et al. (2008) showed that achenes tend to be dispersed within a range of 100 meters, with most of the achenes being deposited at 5.2 meters distance from the parent plant. About 6% of the achenes were uplifted in the experiment; a similar fraction per plant may thus be carried by air currents over longer distances.
Vector Transmission (Biotic)
Humans and their animals transport achenes (Werner et al., 1991; Ernst, 1998), as they readily attach to rough surfaces.
Agricultural practice is unlikely to disperse S. inaequidens, except by attachment of achenes to agricultural machinery.
S. inaequidens may be accidentally dispersed by humans, as a result of the movement of soil during building works, and by attachment of achenes to vehicles or in the slip-stream of road and rail vehicles. Furthermore, wool movement has been important in the past (see History or Introduction/Spread).
Pathway CausesTop of page
Pathway VectorsTop of page
Impact SummaryTop of page
|Cultural/amenity||Positive and negative|
|Economic/livelihood||Positive and negative|
|Fisheries / aquaculture||None|
ImpactTop of page The economic impact of S. inaequidens is minimal, although this may change if the concerns over S. inaequidens in vineyards are realized (Michez, 1994; Mayor, 1996).
Economic ImpactTop of page
Although S. inaequidens occurs frequently along railways and highways, so far no costs other than usual maintenance costs have been reported (Reinhardt et al., 2003). Overall, the current economic impact of S. inaequidens is minimal, but this can be expected to change as S. inaequidens is in the process of colonizing heavily grazed grasslands in southern Europe (Scherber et al., 2003), as well as vineyards (Michez, 1994; Mayor, 1996). It has been observed that S. inaequidens can be poisonous to cows, sheep (Dimande et al., 2007) and horses (Passemard and Priymenko, 2007); if it spreads further into arable land this could cause significant economic impacts.
Environmental ImpactTop of page
Impact on Habitats
No negative impacts on habitats are known for S. inaequidens (Nehring et al., 2013).
Impacts on Biodiversity
No direct impact of S. inaequidens on biodiversity has been reported, probably because the species has so far colonized mainly ruderal habitats (Nehring et al., 2013). Experiments suggest that S. inaequidens does not have any allelopathic effects on other species (Medina et al., 2003; Weisshuhn and Prati, 2009). In the invaded range in Europe, the presence of S. inaequidens does not seem to have an influence on pollinator visiting rates or seed set in the native relative Jacobaea vulgaris (Vanparys et al., 2011).
Social ImpactTop of page
Judging from the available literature it is quite probable that S. inaequidens is able to cause human health problems. The aetiology of pyrrolizidine alkaloid (PA) poisoning in humans was first described by Wilmont and Robertson (1920) in respect to wheat flour contaminated with leaves and achenes of S. ilicifolius and S. burchellii. Human disease caused by PA toxicity is endemic to Central Asia (Anon., 1988) and PA poisoning from S. vulgaris achenes was reported in 1994 in a group of Bedouins in northern Iraq (Altaee and Mahmood, 1998). There appear to be no cases of human death caused by the PAs derived from consumption of S. inaequidens.
Risk and Impact FactorsTop of page Invasiveness
- Proved invasive outside its native range
- Highly adaptable to different environments
- Tolerates, or benefits from, cultivation, browsing pressure, mutilation, fire etc
- Highly mobile locally
- Has high reproductive potential
- Has propagules that can remain viable for more than one year
- Negatively impacts animal health
- Negatively impacts tourism
- Reduced amenity values
- Difficult to identify/detect as a commodity contaminant
- Difficult/costly to control
UsesTop of page
In Europe, S. inaequidens is frequent along highways and railroad tracks and dominates the aspect during its flowering period (Reinhardt et al., 2003).
S. inaequidens is an important food plant for wild insect species in its introduced range (Schmitz and Werner, 2001).
Similarities to Other Species/ConditionsTop of page The morphological variability of S. inaequidens means that it may be confused with other Senecio species in its native range. However, it is unlikely to be confused with other Senecio species in its exotic range. In its native range, on the basis of limited sampling, Radford et al. (2000) indicate that S. madagascariensis can be distinguished from S. inaequidens by its smaller achenes (1.5-2.0 mm long versus 2.6 mm), with hairs confined to the achene grooves, in contrast to the completely hairy achenes of S. inaequidens (although Hilliard (1977) states that the achenes of S. inaequidens are only hairy between the ribs). Hilliard (1977) separates S. inaequidens and S. madagascariensis on the basis of inflorescence size, habit and habitat. S. madagascariensis is a diploid (2n=2x=20; Sindel et al., 1998), whilst S. inaequidens is a tetraploid (2n=4x=40; Radford et al., 2000). Hilliard (1977) also highlights the similiarity of S. harveianus to S. inaequidens, being distinguished on the basis of inflorescence size and calyculus bract number (see Notes on Taxonomy and Nomenclature). However, in the absence of more detailed comparative morphological investigations which comprise material that samples the full range of variation in these presumed taxa, these differences must be treated with caution.
S. inaequidens has superficial similarity to S. lythroides (syn. S. linifolius) in Spain and Morocco and, in the Mediterranean, might also be confused with Plantago arenaria (Plantaginaceae). However, P. arenaria can readily be distinguished from S. inaequidens by the absence of capitula and yellow ray florets and the occurrence of opposite, whorled leaves. S. inaequidens cannot be confused with other native Senecio species in the northern part of its exotic range.
Prevention and ControlTop of page
For areas where S. inaequidens is likely to invade, Cano et al. (2007) suggested surveying open shrublands and grasslands after periods of rainfall. The authors also found that disturbance is likely to enhance the spread of the species in grasslands as well as shrublands and forests.
In Colombia, pasture restoration measurements led to a decrease of S. inaequidens cover from 38% to 1%. Arrieta (2004) showed that mowing every 45 days led to a 20% reduction of seeds in the soil. The two bio-control agents Homeosoma oconequensis and Ensina hyallipennis reduced an S. inaequidens population by 50% in the Colombian Andean region (Arrieta, 2004). Removal by hand has also been shown to be effective (Arrieta, 2004). Competition and rabbit grazing significantly reduced growth and reproduction of S. inaequidens in an experiment (Scherber et al., 2003), but regrowth shoots seem to be unpalatable for rabbits.
If chemical control is applied to the plant, Arrieta (2004) suggested applying the chemicals earlier than 40 days after germination, because at this stage a rosette structure is formed that makes the plant more resistant to phenoxid, benzoic, picolinic acid and isoxazolidone herbicides.
Gaps in Knowledge/Research NeedsTop of page
Given the high risk of health problems connected to the projected spread of S. inaequidens into arable land, there are four groups of questions that need to be addressed urgently:
1) Is the spread of S. inaequidens into pastures and grasslands highly probable in all invaded areas? Can the result of the range modelling presented by Vacchiano et al. (2013) for Italy be generalized for other invaded regions?
2) In which scenarios could S. inaequidens cause human health problems? Are the secondary compounds of S. inaequidens really poisonous to humans? Which parts of the plant have to be consumed, and in what quantities, to cause health problems?
3) In its native range as well as in Colombia, the species already seems to be present in grasslands. Does this cause economic and health problems? What lessons can be learned from the situations there?
4) In case further research confirms the high risk of economic and health problems, there is an urgent need for research on feasible control methods.
To understand the genetics, systematics and morphological variation of S. inaequidens, it is necessary to investigate populations from the exotic ranges of S. inaequidens and S. madagascariensis in more detail, together with material from southern Africa of S. madagascariensis, S. inaequidens, S. burchellii, S. pellucidus, S. skirrhodon and S. harveianus.
ReferencesTop of page
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ContributorsTop of page
02/07/14 Datasheet updated by:
Tina Heger, Technische Universität München, Germany
Distribution MapsTop of page
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