Polygala myrtifolia var. myrtifolia

(Myrtle-leaf Milkwork, Parrot Bush)

This escaped garden plant can often be seen as large swards, especially in coastal areas, where it chokes out indigenous vegetation.

Originally from South Africa's Cape region, this plant is now a problem in New South Wales, South Australia, Tasmania, Victoria, and Western Australia. It is banned in New Zealand but still permitted entry to Australia.

The plant is not usually sold in nurseries but the variety Polygala myrtifolia var. grandiflora, which it closely resembles, is still widely sold in many nurseries, supermarkets and florists. It was once thought to be sterile but this is not the case. It is now recorded as being able to set seed, so it should not be grown.

Not only does Polygala invade coastal vegetation, but other environments as well, such as grassland, grassy woodland, mallee shrubland and riparian environments.

Description

Polygala is a woody shrub that can grow to about 4 metres tall. The invasive clumps it forms can be seen here.

The purple pea flowers are its most recognisable feature. These are produced throughout most of the year but mainly from August through summer. The flowers appear in clusters at the tips of branches and are about 1.5 to 4cm long.

Following flowering, two-celled flattened capsules develop that ripen from green to papery brown. These are oblong and about 5mm long.

The leaves are green and oval shaped, about 5 - 20mm long and the tip can be rounded or blunt. Young stems are purplish with short curly hairs, but older stems are smooth and woody.

Spread

It reproduces by seed, in fact up to 2000 seedlings have been known to germinate per square metre! Competition reduces this to 12 to 30 plants after the first year, which is still a lot of plants per square metre.

Seed is spread by water, birds, ants, dumped garden waste, and even equipment used at the beach, such as surfboards and towels can help spread seed.

The seeds are long lived and can even germinate in heavy shade. Germination usually takes place in autumn but it can happen at any time providing sufficient moisture is available.

Control

The plant is killed by fire and does not readily regrow from roots or cut stumps. However, fire and disturbance will also stimulate dormant seed to germinate, so control can take many years.

Information sources:

Blood, K., 2001, Environmental Weeds - A field guide for SE Australia, published by CH Jerram Science Publishers.

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