Lantana camera is a pleasant-looking annual. You may have come across at the local garden centre. It could fill that hole in the border ... and do the job well with its pretty flowers. Shame it's not a perennial you might think.
However, give that plant its ideal growing conditions and it's another story.
In the 1840s, Lantana camera was introduced as an ornamental plant into the Sydney and Brisbane garden markets. By the 1860s it had naturalised, having thrived under the tropical and sub-tropical growing conditions of Eastern Australia.
Fast forward to today and Lantana covers more than 4 million hectares of land across Australia. It causes such damage, it's recognised as a Weed of National Significance (WoNS) impacting primary industries, conservation and biodiversity. It's poisonous (indeed deadly) to livestock and competes with tree seedlings and other native flora for light and nutrients, severely limiting natural vegetation.
Where conditions are ideal for its growth, it's a brute.
And yet, Lantana camera is the exception. In the UK where, through generations of collectors, we have had more plant introductions from abroad than most, a general rule of thumb is that 10% of all plants introduced to the country go on to 'escape' to some extent. Of these around 90% survive, provided they continue to be replenished by new imported stock. But only 10% create genuinely self-sustaining populations in the wild. And then only 10% of those go on to be regarded (at least by some) as pests i.e. one in a thousand are seen as a problem.
Put another way, and here I am indebted to Ken Thomas, author of 'Where do Camels belong? The story and science of invasive species', of some 12,500 species of plants introduced to the UK, only about 200 count as fully established. 'The number of alien plants troublesome enough to be described as pests depends on your level of tolerance, may be as few as 11 or or as many as 39'.
Anyone plagued, for example, by a Japanese knotweed will tell you one is more than enough. But I believe the sustaining role gardens play in supporting biodiversity far outweigh the risks of introducing troublesome alien species. Care and control where problems arise is of course needed. But far more damage has been done by commercial interests through land clearance, intensive agriculture, use of pesticides etc. than by any plant-collecting and cultivating gardeners. And the ethos of gardening and encouraging biodiversity - the awareness and practice - are of fundamental importance.
Contrast the story of the Lantana with that of the almost extinct Australian Wollemi pine, whose future has been secured via the garden market, or the efforts so many gardeners are making to help sustain vital pollinating bee populations, and it's clear to me that gardeners and the diversity they nourish are very much a good thing.