Invasiveness Assessment - Large flowered St John's wort (Hypericum calycinum) 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 Large flowered St John's wort.

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: Large flowered St John's wort
Scientific name: Hypericum calycinum

Question	Comments	Rating	Confidence
Establishment
Germination requirements?	‘Germination usually takes place .. at 10°C’ (PFAF n.d.). Requires seasonal temperatures.	MH	M
Establishment requirements?	‘It can grow in full shade (deep woodland) semi-shade (light woodland) or no shade’ but flowers better in sun (PFAF n.d.). Can establish without additional factors.	H	M
How much disturbance is required?	Can be found in grassland, forest edges, disturbed sites (Weber 2003). Can establish in relatively intact natural ecosystems.	MH	MH
Growth/Competitive
Life form?	Small shrub (Weber 2003). Life form – other.	L	MH
Allelopathic properties?	None described in Weber (2003).	L	MH
Tolerates herb pressure?	In California, the chrysomelid beetle, Chrysolina quadrigemina, was found to attack H. calycinum (Van Klinken & Edwards 2002). In ‘H. calycinum, the same chemical not only attracts pollinating insects but also deters herbivores that pose a threat to its survival’ (Gronquist et al 2001). Score as medium high as is consumed in California but generally not eaten by animals or insects.	MH	H
Normal growth rate?	Grows ‘at a fast rate’ (PFAF n.d.). Assume that growth will equal competitive species of same life form.	MH	M
Stress tolerance to frost, drought, w/logg, sal. etc?	‘A drought-resistant and fire-tolerant species’ (Weber 2003). Can grow in sandy soils (PFAF n.d.). ‘A very cold-hardy plant, tolerating temperatures down to about -25°C (PFAF n.d.). Not documented as to whether plant can withstand waterlogging.	MH	MH
Reproduction
Reproductive system	Has rhizomes (Weber 2003). Both cross and self-pollinated (PFAF n.d.). Both vegetative and sexual reproduction.	H	MH
Number of propagules produced?	Propagules produced per flowering event not documented. Spreads more through rhizomes. Has ‘extensively creeping rhizomes’ (Weber 2003). Score as medium.	M	MH
Propagule longevity?	Mainly reproduces vegetatively. No documented information on seed viability. Score as low.	L	L
Reproductive period?	‘.. forms dense colonies due to the extensively creeping rhizomes’ (Weber 2003). Capable of forming dense monocultures.	H	MH
Time to reproductive maturity?	Time to reproductive maturity is not documented. Score as medium.	M	L
Dispersal
Number of mechanisms?	No evidence of how propagules are spread. Mainly spread by gravity.	L	L
How far do they disperse?	Unlikely that propagules will disperse greater than 200 m.	L	L

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