These pretty, purple flowers with a deceptively pleasant name are becoming a problem in Australia.
Polygala, sold under innocent-sounding labels as "sweet pea", "Bellerine pea" and "parrot bush", is overtaking large tracts of Australia's coastline.
That has prompted the Invasive Species Council to nominate Polygala myrtifolia (also known as myrtle-leaf milkwort) as one of Australia's most significant weeds, even as potted examples continue to line shelves in retail stores.
Polygala is routinely sold at Bunnings and other retail chains.
Invasive Species Council policy director Carol Booth said the thick shrub, originally from southern Africa, had colonised the south-eastern Australian coastline at the expense of native flora.
"It just takes over," Dr Booth explained.
The Invasive Species Council targeted Bunnings last year for stocking gazania seeds.
Gazania, banned in South Australia and recognised as an environmental weed in Victoria, Tasmania, Queensland, and New South Wales, is still permitted to be sold in most states.
ABC News found packets of gazania in a Victorian store when it discovered the rows of potted polygala.
Bunnings has confirmed Polygala myrtifolia and its hybrids are sold through nurseries and plant retailers across Australia but that it focused on selling hybrid polygala, which differs from Polygala myrtifolia.
The hardware and gardening retailer said it would continue to monitor invasive weed regulations, update its products accordingly and customers should read plant label descriptions before buying.
A growing problem
Australia has a government-endorsed list of 32 Weeds of National Significance (WONS), which threaten the nation's agriculture and environment.
Dr Booth said the list needed updating to include milkwort and other plant varieties that threaten Australia's biodiversity.
At the very least, milkwort should be added to a list of plants banned for sale in Australia, she said.
"It's not aligned with risk, it's not focused on preventing most invasions and it's not in the public interest," she said.
The Invasive Species Council estimates about 3,000 introduced plant species have naturalised in Australia.
That means about one in nine species growing in the wild is not native to that area.
More than 1,000 are considered invasive, which means they cause harm to native species and ecosystems.
"Australia's got a huge weed problem. It's our most expensive land management problem, our most expensive nature conservation problem," Dr Booth said.
"Most plants that can cause harm out in the wild are still available for sale.
We will fight them on the beaches
The characteristics that make polygala popular with suburban gardeners as a ground-covering shrub – hardiness and an ability to survive and thrive in dunes, rocky outcrops, and other marginal environments – also ensure it is especially difficult to remove once established.
Volunteer groups, including Nepean Peninsula Landcare, are on the front line of efforts to control the invasive bush, and say it is an uphill battle.
"If you come down to the Mornington Peninsula, you can't miss it. You don't have to look for it, it's everywhere," Nepean Peninsula Landcare volunteer John Dewhurst said.
"It is the most dominant plant through the coastal dune systems and all along the foreshore.
Polygala is found along Australia's southern coastline, from Western Australia through South Australia, Victoria and the New South Wales coast.
There are two ways to remove the weed, but each has its drawbacks.
Herbicides may be effective but are expensive and have the potential to damage native flora.
The most practical way to deal with milkwort is to remove it manually, which is time-consuming and exhausting for the volunteers.
That's prompted Nepean Peninsula Landcare and the Invasive Species Council to investigate a potential biological control.
"We have engaged some expert scientists, both in Australia and South Africa, to try to find a biocontrol for Polygala," Mr Dewhurst said.
"It's called 'the Poly Gone project' and that involves locating insects or fungus in South Africa where it comes from that control it naturally.
"Whenever you mention the word 'biocontrol', people think cane toad, but there've been many, many successful biocontrols introduced into Australia, like the prickly pear moth.
"The research is being done in South Africa to ensure it's safe before something happens here."
More weeds of national significance
In 1999, Australia's federal and state governments nominated their original 20 weeds of national significance (WONS) that represented the greatest threat to Australian agriculture and the environment.
A further 12 were added in 2012.
The National Biosecurity Committee, made up of Australian Department of Agriculture, Fisheries and Forestry representatives, plus others from each state and territory government, was in the process of adding new weeds to the WONS list, said Dr Booth.
Those prioritised as potential weeds of national significance include:
African lovegrass (Eragrostis curvula)
European olive (Olea europaea)
Amazon frogbit (Limnobium laevigatum)
Ox-eye daisy (Leucanthemum vulgare)
Arum lily (Zantedeschia aethiopica)
Sea spurge (Euphorbia paralias)
Calotrope (rubber bush) (Calotropis procera)
Siam weed (Chromolaena odorata)
Giant rat's tail grass (Sporobolus pyramidalis)
Spanish heath (Erica lusitanica)
Harrisia (Harrisia martinii)
Tropical soda apple (Solanum viarum)
Neem tree (Azadirachta indica)
Wandering trad (Tradescantia fluminensis)
"The list will grow but it's only a very small proportion of the weeds that really are nationally significant, so it's ultimately the ones which state and territory governments agree to put some money into coordinating control," Dr Booth said.
"Unfortunately, we have got so many more than this small list of species that really warrant substantial control," he said.
