The white sap from this common weed, also known as petty spurge, was described by Nicolas Culpeper’s Complete Herbalist (1826) as “a good treatment for warts”.

Don’t try this at home, however, as its also an irritant.

Milkweed made its way from its native Europe to Australia, where biochemist Dr Jim Aylward had it in his garden.

“My mum grew it for 20 years and swore by it,” he says.

“She always told me to put it on my skin to help sunspots.”

In 1997, Dr Aylward isolated its active ingredient, ingenol mebutate, which he discovered was toxic to rapidly replicating human tissue.

And recent clinical trials of Picato, a gel derived from milkweed sap, suggest it is effective at stopping lesions turning into skin cancer.