TALL and leafy, it might look like an attractive plant, but it can claw its way through concrete, fell walls with little trouble, and it is making homeowners' lives a misery.
You will have seen Japanese knotweed standing erect and strong in parks and green spaces, by ponds and in gardens all across Swansea Bay. Its spread is speedy, far reaching and very, very expensive – slashing thousands off sellers' asking prices, stimying mortgage applications and undermining foundations.
Morriston homeowner Joy Richards knows all about the misery it can cause.
She has been so demoralised by the uninvited invader in her front garden that she has taken her Trewyddfa Road home off the market three times, since buyers and mortgage firms run a mile when they spot its confident form.
"The last time I had my home valued they suggested I cut the asking price by half. It is terrible.
"Japanese knotweed is the Godzilla of weeds," she says. "It really is a curse. And I feel defeated by it.
"I am getting older. I have arthritis and although I love my home and I have put a lot of work in to it, I need to move because I can't maintain the garden now."
When she bought the house around a decade ago Joy's survey didn't pick up the knotweed at the end of the garden and though she saw the plant there at the time, she wasn't aware of its virulence.
These days it is an epidemic which some experts claim could take 50 years to eradicate in Swansea, even if nuclear-strength efforts were made to stamp it out.
And according to a new Commonwealth Agriculture Bureaux International report, Swansea is considered to be one of the worst affected parts of the UK, with the total biomass of the plant estimated to exceed 62,000 tonnes. AM for the city's East constituency, Mike Hedges, has taken up the issue and he spoke at a debate on an inquiry into invasive non-native species in the Senedd this month about it.
"The overall infestation in Swansea has been estimated to cost about £9.5 million in chemical treatment, and will take approximately 50 years to eradicate using conventional methods and current treatment rates, and that's without taking into consideration its spread to new areas.
"There are few lenders who will finance the purchase of property if knotweed is present in the garden, in a neighbouring property or, more likely, in the area, often on land of unknown ownership," he said.
"This is causing difficulty for those looking to sell and get a mortgage. The presence of knotweed devalues a property massively and causes huge problems to the people concerned."
Mr Hedges told the meeting Swansea Council alone had spent around £200,000 in the past 10 years trying to control knotweed.
The Welsh Government is part-funding a two-year trial at Swansea University to examine the chemical control of knotweed. But if you are an anxious householder, like Joy, it is likely you are tackling it alone.
At the moment she pays an eradication specialist £300 a pop to spray vicious chemicals at the weed in her garden. But it comes back swiftly, and with vigour.
The plant thrives on disturbance. The tiniest sliver of stem can regrow, and it can be spread both by natural means and by human activity.
"The problem is that even if you have it treated," says Joy, "If there is some in your neighbours' garden, or on land next to your home, it just spreads across and you are back to the beginning again. If you pull it up it spreads spores around so it seeds itself. It is horrible stuff. And you aren't legally allowed to dispose of it at the tip unless you are registered to do that."
It is a sorry tale. And it is a cautionary tale too.
Japanese knotweed — fallopia japonica — seemed like such a good idea at the time. Back in the mid-19th century, Britain's gardeners were on the lookout for new, attractive species from abroad which would be easy to grow and which would add a splash of exotic colour to the native horticultural palate.
But no one thinks Japanese knotweed is lovely now.
From a handful of sites in the 1850s, this Oriental menace has now spread to almost every corner of the land, unchecked, seemingly unstoppable, strangling the life out of native ecosystems.
And we are living to regret their choice of knotweed.
Joy says while her own story, and that of hundreds of others is very upsetting, it is an issue that the country as whole needs to wise up about.
She adds: "So many people can't sell their homes because of Japanese knotweed. What is that doing to the Welsh economy? If knotweed is on land that could be developed, how is that going to affect planning permission? We have to do something about this."