Our Geike Gorge Guide, at Geike Gorge in the Kimberley, called Calotropis procera Camel Cabbage, because, she said, it was introduced and distributed around Australia as camel food and presumably because the leaves look a bit like a cabbage.
The common names I've found in a quick search are Calotropis, Rubber Bush, Kapock Tree and even Apple of Sodom, but not Camel Cabbage.
It stands out from the local flora, with its large greyish leaves, looking a bit like one of those bid leaved banksias in Western Australia. But this plant is more exotic than that, hailing from tropical Asia and Africa.
In Australia Camel Cabbage, as I like to call it, has a patchy distribution across central and northern Australia, with one of those patches in the western Kimberley. According to the Weeds Australia site, it has the potential to spread far more widely across pretty much all of northern and middle Australia, but not the coastal areas outside the true tropics.
My reason for illustrating and mentioning this plant here is that it intrigued me as I drove past and I just couldn't work out what it was. When I stopped and looked at the flowers I was further perplexed, although once identified, I can see that it belongs to the Asclepiadaceae (or perhaps a subfamily within the Apocynaceae) with its milky sap and flowers like a Hoya.
But what pretty flowers! If only it was a native.
I gather the sees are transported by wind and by water, the latter being in great abundance when I was at Geike Gorge in the so-called dry season...
Like much of the Asclepiadaceae, it is highly toxic to humans and probably other animals, such as cattle but presumably not camels.
A paper published in The Rangeland Journal last year by a research group from Queensland led by Joseph Vitelli tested nearly a dozen herbicides and they all worked pretty well in killing the plant. Once the plants are knocked out, they suggest planting (in pastures) perennial grasses to outcompete the 'cabbage' seedlings, followed up by a little more chemical control.
A pretty tough treatment for a pretty weed.