Invasiveness Assessment - Gazania (Gazania rigens) 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 Gazania.

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: Gazania
Scientific name: Gazania rigens

Question	Comments	Rating	Confidence
Establishment
Germination requirements?	Gazanias in general germinate or spread vegetatively whenever conditions suit (DeLaine & Stokes, 2006). Grow from seed in March or April (van der Spuy, 1971). Require seasonal temperatures.	MH	MH
Establishment requirements?	Tolerates full sun to light shade (MSWN, 2005). Can establish under moderate canopy cover.	MH	M
How much disturbance is required?	In its native range, in southern Africa, it is a strand plant [occurs up to the edge of stabilised dunes or inland vegetation] (Ross, 1972) and is a common sand coloniser (Pooley, 1988). It inhabits roadsides and coastal waste land, usually in sandy soils in NZ (Webb et al, 1988). In Australia, it appears to be confined to coastal dunes (Groves et al, 2005; Faithfull, 2006; D. Cooke, pers. comm.). Major disturbance required with little or no competition from other species.	L	MH
Growth/Competitive
Life form?	Perennial with rhizomatous, creeping stems, recorded as growing in terrestrial environments (Faithfull, 2006). Geophyte.	ML	MH
Allelopathic properties?	May have allelopathic properties, as Gazania patches are always bare of other plants (Cordingley & Petherick, 2005). Major allelopathic properties.	H	M
Tolerates herb pressure?	Plants heavily damaged by rabbits (Metzger & Weisberg, 2001). Heavy damage implies that this species is preferred by rabbits; however, the plant may persist due to its rhizomatous nature.	ML	M
Normal growth rate?	A later coloniser of coastal dunes “with slower growth” than another hummock plant (Elliot et al, 2000). “Moderately fast” growing (MSWN, 2005). Evidence about growth rate is mixed.	M	L
Stress tolerance to frost, drought, w/logg, sal. etc?	“Grows well in dry districts and…tolerates quite severe frosts” (van der Spuy, 1971). Tolerates some soil dryness, but overly moist soils can lead to root and stem rot (MBG, 2006); requires good drainage (MSWN, 2005). A strand plant, “often [found] on the seaward side of the first line of dunes” (Hilliard, 1977); withstands salt-laden winds (Groves et al, 2005). Likely to be highly tolerant of salinity, drought and frost. Not tolerant of waterlogging.	MH	MH
Reproduction
Reproductive system	“Produces abundant wind-blown seeds and spreads rapidly. It also spreads vegetatively…It is often spread in garden waste” (Groves et al, 2005). Stems tend to take root at the nodes (Richardson & Richardson, 2006). Can be propagated from stem cuttings (Page & Olds, 1997). Both vegetative and sexual reproduction.	H	MH
Number of propagules produced?	Abundant (Faithfull, 2006). Detailed photographs of the plant show more than 40 seeds per seed head (Tübingen University, 2005). Photographs of the plant in the landscape show more than 75 flower heads per plant (Landscape Resources, 2007). 75 x 40 = 3,000. More than 2000 seeds per plant.	H	M
Propagule longevity?	Unknown.	M	L
Reproductive period?	Considered as either an annual or short-lived perennial (Tippette, 2002). No further evidence found.	M	L
Time to reproductive maturity?	Able to flower 12 weeks after seed is sown (McCulley & McCulley, 2002). Gazanias in general grown in a hothouse, are capable of flowering within 4 months (Ball, 1985). Reaches reproductive maturity in less than one year.	H	MH
Dispersal
Number of mechanisms?	“Seeds spread by water and wind” (Blood, 2001). Gazania seeds in general carried by water (DeLaine & Stokes, 2006).	MH	MH
How far do they disperse?	Most propagules, spread by water and wind (Blood, 2001), could disperse 20-200 m, with few to none likely to disperse to 1 km.	ML	M

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