Invasiveness Assessment - Bulbil watsonia (Watsonia meriana) 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 Bulbil watsonia.

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: Bulbil watsonia
Scientific name: Watsonia meriana
*“Watsonia meriana cv bulbillefera is a cormous perennial native to Southern Africa & also known as W. bulbillefera J. Mathews & L. Bolus”. (Wilson & Conran 1993).

Question	Comments	Reference	Rating
Establishment
Germination requirements?	Corms and cormils germinate in late autumn.	P & C (1992)	MH
Establishment requirements?	Mostly occurs in ‘open’ habitats (e.g. pastures, roadsides, neglected areas, grasslands).	P & C (1992) Carr et al (1992)	ML
How much disturbance is required?	Establishes in minor disturbed natural ecosystems (e.g. ‘lowland grassland and grassy woodland’), and pasture. Cooke (1998)	P & C (1992) Carr et al (1992)	MH
Growth/Competitive
Life form?	Erect perennial herb, reproducing from corms and cormils geophyte.	P & C (1992) Carr et al (1992)	ML
Allelopathic properties?	None described.		L
Tolerates herb pressure?	“Animals do not graze mature plants but young shoots are eaten”.	P & C (1992)	MH
Normal growth rate?	“Highly competitive in cleared areas on heavy soil…can build up dense colonies which exclude other species”.	APCC (1992)	MH
Stress tolerance to frost, drought, w/logg, sal. etc?	Tolerant of water logging, drought (occurs dry areas of Western Australia), fire (re-grows from underground structures, frost (occurs in Southern Tasmania).	P & C (1992) Blood (1997)	MH
Reproduction
Reproductive system	Reproducing from corms and cormils. Also reproducing from seed.	P & C (1992 RPPSWG (1991)	H
Number of propagules produced?	Estimate based on pictures and descriptions: 15 flowers per plant x 10 seeds per flower = 75.		ML
Propagule longevity?	?		M
Reproductive period?	Aerial growth does annually (in summer), however re grows from corms. Some corms have been observed with 35 plates, indicating the minimum age of some Watsonia ‘stands’. (Wilson & Conran 1993).	P & C (1992	H
Time to reproductive maturity?	Plants developing from cormils do not flower in first year, but in either the second or third year.	P & C (1992	ML
Dispersal
Number of mechanisms?	Corms and cormils – graders and other earth moving equipment.	P & C (1992	MH
How far do they disperse?	“Seeds and bulbils usually fall to the ground and germinate next to the parent plant, resulting in a slow expansion of an existing infestation”. (RPPSWG 1991).		L

* APCC – Animal and Plant Control Commission (1992) * RPPSWG – Regional Pest Plant Strategy Working Group (1991)

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