Invasiveness Assessment - Skeleton weed (Chondrilla juncea) in Victoria (Nox)

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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 Skeleton weed.

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 - 1 MB)
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Common Name: Skeleton weed
Scientific name: Chondrilla juncea

Question	Comments	Reference	Rating
Establishment
Germination requirements?	Seeds germinate after autumn rains.	P&C (1992)	MH
Establishment requirements?	Can establish under moderate canopy cover (See details of experiment by McVean (1966) p.355).	McVean (1966)	MH
How much disturbance is required?	Establishes in relatively healthy natural ecosystems e.g. mallee shrubland, Wyperfield N.P.	Carr et al (1992) McVean (1966)	H
Growth/Competitive
Life form?	An erect, much branched perennial herb. Geophyte → aerial growth dies autumn, new rosettes autumn/winter.	P&C (1992)	ML
Allelopathic properties?	None described.		L
Tolerates herb pressure?	Biocontrol agents. “Once established, the plant will survive any amount of cutting.” The stems prior to flowering are palatable to sheep & other domestic animals while goats & wild herbivores will consume the older, more fibrous stems also (McVean 1966). Plants may be prevented from flowering where animal browsing is constant. (McVean 1966). – Should/assumed to be capable of flowering under mod herbivory.	P&C (1992)	MH
Normal growth rate?	Very competitive in cereal crops, but subterranean clover can be an effective competitor with established skeleton weed.	P&C (1992) McVean (1966)	MH
Stress tolerance to frost, drought, w/logg, sal. etc?	Tolerance to drought, frost, waterlogging.	P&C (1992) CWMA (2000)	MH
Reproduction
Reproductive system	Reproducing from a long taproot & by seed.	P&C (1992)	H
Number of propagules produced?	A single plant can product >27,000 seeds in a season, although the average is much less	P&C (1992)	H
Propagule longevity?	Seeds are relatively short-lived and probably do not survive > 6 months	P&C (1992)	L
Reproductive period?	Long-lived perennial. Forms ‘dense colonies’.	P&C (1992)	H
Time to reproductive maturity?	Germination in autumn (March-April-May), with the main flowering period beginning in mid to late December throughout Australia.	McVean (1966)	H
Dispersal
Number of mechanisms?	Wind, wool, fabric, machinery, vehicles, railway trucks, contaminated hay & chaff, seed-harvesting ants.	P&C (1992)	H
How far do they disperse?	Parachute like seeds easily spread by wind.	PBCMAF (1988) Champion (1995)	MH

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