Invasiveness Assessment - Spotted thistle (Scolymus maculatus) 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 Spotted thistle.

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: Spotted thistle
Scientific name: Scolymus maculatus

Question	Comments	Rating	Confidence
Establishment
Germination requirements?	Germinate in autumn or early winter (Parsons & Cuthbertson, 1992). Natural seasonal disturbance required.	MH	MH
Establishment requirements?	“Can grow in semi-shade (light woodland) or no shade (PFAF, 2000). Can establish without access to direct light.	H	M
How much disturbance is required?	“Weed of disturbed sites, mainly in arable fields and waste places” (Parsons & Cuthbertson, 1992). “Uncultivated land, in abandoned fields and ditches and along paths and waysides” (Neuz & Bermejo, 1994). Waysides and cornfields (PFAF, 2000). Establishes in highly disturbed sites.	ML	H
Growth/Competitive
Life form?	Annual herb to 50-100 cm (Parsons & Cuthbertson, 1992).	L	MH
Allelopathic properties?	None found recorded.	L	L
Tolerates herb pressure?	“Aerial growth is not eaten because of the spines…even sparse stands are avoided by stock” (Parsons & Cuthbertson, 1992). “Nothing will either eat it or approach it” (Maiden, 1908).	H	H
Normal growth rate?	Young plants produce a “slowly developing rosette” from autumn or early winter and then “much branched stems form in late winter” (Parsons & Cuthbertson, 1992). “With hot temperatures the plant grows very rapidly, with the basal rosette forming quickly” (Neuz & Bermejo, 1994). Annual herb to 50-100 cm (Parsons & Cuthbertson, 1992).This herb reaches an average height for an annual.	MH	MH
Stress tolerance to frost, drought, w/logg, sal. etc?	“Tolerates cold and drought” (Neuz & Bermejo, 1994). Danin (2005) records this plant growing in winter water-logged soils. Hardy to zone 7 (PFAF) –16ºC - 12ºC. Halophytic [salt-tolerant] (UNEP-WCMC, 2005). Highly tolerant to frost, and some tolerance to drought, salinity and seasonal water-logging	M	M
Reproduction
Reproductive system	Seed (Parsons & Cuthbertson, 1992). Hermaphrodite flowers (PFAF, 2000). No further information was found but there is the potential for cross- and self-fertilisation with hermaphrodite flowers.	ML	M
Number of propagules produced?	“Capitula…solitary or in clusters of two to four” (Neuz & Bermejo, 1994). Picture of mature plant shows at least 55 capitula (Parsons & Cuthbertson, 2002), and a photograph (Wikipedia, 2006) shows a capitulum with at least 20 florets. 55 x 20 = 1,100 propagules.	MH	ML
Propagule longevity?	“Germination capacity is maintained for a long time” (Neuz & Bermejo, 1994).	M	H
Reproductive period?	Annual herb (Parsons & Cuthbertson, 1992).	L	MH
Time to reproductive maturity?	“Seeds germinate in autumn or early winter…aerial growth dies in late summer after seeds have matured” (Parsons & Cuthbertson, 1992). Less than a year.	H	MH
Dispersal
Number of mechanisms?	Whole plants transported by wind and water and “spiny seed head catches in wool” and the plant is “present along the stock route from Breeza through Warrah to Merriwa” (Parsons & Cuthbertson, 1992), indicating transport by animals (externally)	MH	MH
How far do they disperse?	“Aerial growth dies…after seeds have matured and, breaking off at the base, blows away much like a tumbleweed, shedding seeds as it goes…some plants, blown into creeks or rivers, float for long distances…Present along the stock route from Breeza through Warrah to Merriwa”… Seed are “not well adapted to wind dispersal…quite buoyant” Spiny seed heads catch in wool and contaminate fodder (Parsons & Cuthbertson, 1992). Transport by floating and attached to animals makes it likely that some propagules will disperse greater than 1 km.	H	MH

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