Invasiveness Assessment - Myrtle-leaf milkwort (Polygala myrtifolia) 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 Myrtle-leaf milkwort.
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: Myrtle-leaf milkwort
Scientific name: Polygala myrtifolia
| Question | Comments | Rating | Confidence |
| Establishment | |||
| Germination requirements? | Seeds germinate in the open or under dense vegetation generally in May to June (Carter et al, 1990) but at any time of the year if sufficient moisture (Blood, 2001). However Arnold (1981) states that the seeds appear to be capable of germinating any time of the year. Seedlings that germinate in autumn tend to have a better survival rate. Germinates prolifically after disturbance such as fire (ESC, 2002) and following soil or canopy disturbance (Muyt, 2001). Seeds are able to germinate throughout the year, whilst there is a seasonal component to survival, this question only deals with germination requirements. | H | MH |
| Establishment requirements? | Occurs in diverse vegetation types and on may different soils (Meerow and Ayala-Silva, 2005). Most growth occurs over the cooler, moist winter period (Muyt, 2001). In South Australia all infestations are coastal, on shallow soils over calcrete or deep calcareous sands (Carter et al, 1990). All sites receive 500-700 mm annual rainfall, predominately in winter (Carter et al, 1990). Establishes in dune systems, coastal bluffs, shrublands and woodlands (Muyt, 2001). It prefers light, sandy, well-drained soils (DPI, 2007). Germinates readily in both full shade and full sun (Muyt, 2001, Carter et al, 1990). The plant is able to establish in a range of conditions but is dependent on moist periods over winter for growth. . | MH | MH |
| How much disturbance is required? | The plant establishes well in disturbed sites (Weber, 2003). Grows in both shade and full sun (Muyt, 2001). Mass germination can occur following soil or canopy disturbance (Muyt, 2001) and fire (ESC, 2002). It is unclear whether this species invades native vegetation or requires disturbed sites. Isolated satellite infestations occur in disturbed areas, extending into relatively undisturbed vegetation as a front (Carter et al, 1990). Can invade dry coastal vegetation, heathland and heathy woodland, mallee shrubland, lowland, grassland and grassy woodland, dry sclerophyll forests and woodland and riparian vegetation (Carr et al, 1992). The plant is able to establish in both disturbed and relatively undisturbed areas. | MH | MH |
| Growth/Competitive | |||
| Life form? | This evergreen shrub reaches a height of 1.25 to 2 m, and maintains a tight, spherical canopy (Meerow and Ayala-Silva, 2005). Small, much branched hairless perennial (Roy et al, 1998). Belongs to the polygalaceae family (Harden, 1993). | L | H |
| Allelopathic properties? | No information found. | M | L |
| Tolerates herb pressure? | It does not tolerate grazing and can only establish in areas where livestock have been excluded (Carter et al 1990). | L | MH |
| Normal growth rate? | It grows rapidly and flowers when still young (ESC, 2002). It’s competing with coastal wattle Acacia longifolia var. sophorae (Carter et al, 1990). It is able to compete with a similar life form suggesting that its growth rate is fairly rapid. | MH | M |
| Stress tolerance to frost, drought, w/logg, sal. etc? | Plants tolerate salt-laden winds, exposed positions and seasonally hot, dry spells (Muyt, 2001). Hot fires kill mature plants, but seedling regeneration is rapid (Carter et al, 1990). It is tolerant of poor soils, dry conditions and exposure to salt (ESC, 2002). It prefers light, sandy, well-drained soils (DPI, 2007). Plant is tolerant to salt, drought and poor soils but is susceptible to fire and possibly waterlogging. | ML | MH |
| Reproduction | |||
| Reproductive system | The peak flowering period is from spring to summer (Sept to Oct) in most areas where it is grown, (Meerow and Ayala-Silva, 2005; Carter et al, 1990, Muyt 2001) plant produces an abundance of 2 to 3 cm long purple flowers. However plant can flower all year round (Roy et al, 1998). Seeds germinate in May to June (Carter et al, 1990). The plant reproduces only by seed (Muyt, 2001). | ML | M |
| Number of propagules produced? | Two seeded capsules about 10 mm long (Roy et al, 1998). Seedling density may exceed 2,000 m2 (Weber, 2003). | MH | M |
| Propagule longevity? | Seeds can remain viable in the soil for two to three years (Weber, 2003, Muyt, 2001). | L | MH |
| Reproductive period? | Can flower and seed when less than 50 cm high (2 years old) (Muyt, 2001; Carter et al, 1990). Older plants are around 15 years old and are still in good condition at this age (van der Walt, 2003). Plant is capable of flowering for more than 10 years. | H | MH |
| Time to reproductive maturity? | Plants are able to set seed at the age of 2 (Muyt, 2001; Carter et al, 1990). | ML | MH |
| Dispersal | |||
| Number of mechanisms? | Seed is dispersed by birds, ants, water, in soil and garden refuse (Muyt, 2001). | H | MH |
| How far do they disperse? | Due to bird dispersal it is very likely that at least one propagule will disperse greater than one kilometre. | H | MH |
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