Invasiveness Assessment - Blue psoralea (Psoralea pinnata) 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 Blue psoralea (blue butterfly bush).

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)
To view the information PDF requires the use of a PDF reader. This can be installed for free from the Adobe website (external link).

Common Name: Blue Psoralea (blue butterfly bush)
Scientific name: Psoralea pinnata

Question	Comments	Rating	Confidence
Establishment
Germination requirements?	Germination is reported to occur in Autumn, especially after fire or another disturbance. The seeds are not dependent on fire for germination however (Blood 2001).	MH	MH
Establishment requirements?	Tolerant of partial shade, invades forest (Blood 2001).	MH	MH
How much disturbance is required?	Highly invasive in heathland (Muyt 2001).	H	MH
Growth/Competitive
Life form?	In the Fabaceae family and can fix nitrogen (Blood 2001). Therefore a legume.	MH	MH
Allelopathic properties?	No allelopathic properties are reported for this species.	L
Tolerates herb pressure?	Tolerant of grazing, used as a fodder source (Blood 2001). Resprouts after being cut at the base (Blood 2001).	MH	MH
Normal growth rate?	Very fast growing (Blood 2001). Can grow rapidly to 1.5 m in a year (Eliovson 1960).	H	H
Stress tolerance to frost, drought, w/logg, sal. etc?	Tolerant of frost, to temperatures of -4ºC (Blood 2001). Tolerant of fire; fire stimulates germination and mature plants can reprout (Blood 2001). Tolerant of dry conditions (Blood 2001). No reported tolerance of drought however. Tolerant of waterlogging; occurs in swamps (Blood 2001). Tolerant of salt laden winds (Muyt 2001).	MH	MH
Reproduction
Reproductive system	Reproduces by seed (Blood 2001).	ML	MH
Number of propagules produced?	Can produce thousands of seeds annually (Muyt 2001).	H	MH
Propagule longevity?	Seeds remain viable for at least 8 years (Muyt 2001).	ML	MH
Reproductive period?	Can live for 15 years (Muyt 2001). Being able to start flowering in its second year as reported by Blood (2001) would give a potential reproductive period of more than 10 years.	H	MH
Time to reproductive maturity?	Can start flowering after 1 year (Eliovson 1960).	MH	H
Dispersal
Number of mechanisms?	Dispersed by water and possibly by birds (Blood 2001). Human aided dispersal includes accidentally through machinery and contaminated soil and deliberately; still occasionally available in trade (Blood 2001; Muyt 2001).	H	MH
How far do they disperse?	Dispersal by water and possibly by birds would enable propagules to move more than 1 km. Dispersal of more than 1 km along a roadside most probably through contaminated machinery has been observed (Mitchard pers comm. 2007).	H	ML

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