Invasiveness Assessment - White weeping broom (Retama raetam) 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 White weeping broom.

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: White weeping broom
Scientific name: Retama raetam

Question	Comments	Rating	Confidence
Establishment
Germination requirements?	“Seeds mainly germinate in autumn, but can germinate year round under suitable conditions” (CRC Weed Management, 2003).	H	M
Establishment requirements?	Invading she-oak woodlands on the Eyre Peninsula and may infest grazing land (CRC Weed Management, 2003). This suggests that it can establish under moderate canopy.	MH	M
How much disturbance is required?	Infests grazing land and invades deserts and grasslands, sheoak woodlands (CRC Weed Management, 2003), stabilized and semi-mobile dunes (Izhaki & Ne’eman, 1997). These ecosystems tend to be minor to highly disturbed.	MH	M
Growth/Competitive
Life form?	Legume (Pnueli et al, 2002).	MH	H
Allelopathic properties?	None recorded.	L	L
Tolerates herb pressure?	“Poisonous and unpalatable” (El-bana et al, 2003). “Cut plants resprout vigorously” CRC Weed Management. However, it is listed as a palatable species in d’Arces, 1961	H	H
Normal growth rate?	Observed growing at 1’ (30 cm) or less per year (Johnson, 2005) which is fairly slow for a shrub.	ML	MH
Stress tolerance to frost, drought, w/logg, sal. etc?	“Extreme drought tolerance” (Pnueli et al, 2002). Halophytic (Liang & Steinberger, 2001). Frost tolerant to at least –9°C but killed by waterlogging (Johnson, 2005). “Fire effectively kills plants…but lightly scorched plants may resprout” (CRC Weed Management, 2003). High tolerance to drought and frost, moderate fire and salt tolerance. Not tolerant of waterlogging.	MH	MH
Reproduction
Reproductive system	Seed. Flower is closed (see picture in CRC Weed Management, 2003), and attract insects (Whitinger, 2006) suggesting cross-pollination is required.	L	M
Number of propagules produced?	“Up to thousands of seeds on larger plants” (CRC Weed Management, 2003).	H	M
Propagule longevity?	“Several years…A hard seed coat renders most seeds dormant initially” (CRC Weed Management, 2003). No specific information found.	M	L
Reproductive period?	Recorded as fruiting over a period of at least 3 years (Johnson, 2005).	MH	MH
Time to reproductive maturity?	Recorded as fruiting 5 years after planting (Johnson, 2005).	ML	MH
Dispersal
Number of mechanisms?	Water (CRC Weed Management, 2003). Ingested by hares (recorded as carry seeds >10 m from parent plant), whose digestive processes stimulate germination (Izhaki & Ne’eman, 1997).	MH	M
How far do they disperse?	Many seeds could be transported by hares (Izhaki & Ne’eman, 1997) 200 –1,000 m.	MH	H

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