Invasiveness Assessment - South African weed-orchid (Disa bracteata) 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 South African weed-orchid.

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: South African weed-orchid
Scientific name: Disa bracteata

Question	Comments	Rating	Confidence
Establishment
Germination requirements?	Sprouts in early spring (DNRE 2002). Requires natural seasonal conditions for germination.	MH	M
Establishment requirements?	Can grow in both shade and open ground (Muyt 2001). Can establish under a moderate canopy.	MH	MH
How much disturbance is required?	Generally grows in disturbed areas and can be found in ‘woodlands, heathlands, roadsides, grazing lands’ (Muyt 2001). ‘Invades bushland and pastures’ (DNRE 2002) .Can establish in minor disturbed ecosystems.	MH	M
Growth/Competitive
Life form?	‘Deciduous perennial terrestrial orchid with underground tubers’ (DNRE 2002). Geophyte	ML	M
Allelopathic properties?	None described.	L	M
Tolerates herb pressure?	Known to be ‘consumed by sheep, cattle, horses and kangaroos’ (Dempster 2005). Capable of seed production under moderate herbivory pressure.	MH	ML
Normal growth rate?	‘Competes and excludes smaller indigenous flora including orchids, lilies and grasses ’ (Muyt 2001). Growth rate will exceed most other species of same life form.	H	MH
Stress tolerance to frost, drought, w/logg, sal. etc?	‘.. tolerant to fire, frost and drought’ (Dempster 2005). No documented evidence of plants response to waterlogging or salinity. Score medium.	M	ML
Reproduction
Reproductive system	Self-pollinated (Muyt 2001). Has tubers (DNRE 2002). Capable of sexual and vegetative reproduction.	H	M
Number of propagules produced?	‘..each capsule containing up to a thousand seeds’ (Muyt 2001). ‘Each plant produces tens of thousands of airborne seeds’ (DNRE 2002).	H	MH
Propagule longevity?	Seeds remain viable for seven years (Muyt 2001).	ML	MH
Reproductive period?	Perennial plant, producing flowers in second or third year (Muyt 2001). No documented evidence that plant produces viable propagules for greater than 10 years.	MH	MH
Time to reproductive maturity?	Produces flower in second or third year (Muyt 2001).	ML	MH
Dispersal
Number of mechanisms?	Known to be both wind and water dispersed. ‘.. likely to be introduced accidentally on vehicles and machinery .. spread by seeds on clothing, shoes and camping equipment’ Seeds are ‘minute and dust-like .. may be blown many km’ (DNRE 2002).	H	M
How far do they disperse?	Estimated that spread in South Australia has averaged 10 km per year. Seeds are ‘minute and dust-like .. may be blown many km’ (DNRE 2002).	H	M

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