Terry gave me a little potted petty spurge which was full grown to about five inches in a few weeks, with green flowers.  I put it outdoors and Mary thought it was a weed, picked it and threw it aside.  I tried to replant it but it was dead.  Apparently it had seeded because in a matter of days there were a dozen baby plants springing up!  They were the genuine thing, yielding a drop of white biologically active sap when a leaf was plucked.

This is Clip One from the on line literature.

Euphorbia peplus (petty spurge,[1][2] radium weed,[2] cancer weed,[2] or milkweed[2]) is a species of Euphorbia, native to most of Europe, northern Africa, and western Asia, where it typically grows in cultivated arable land, gardens, and other disturbed land.[c1][3][4]

Outside of its native range it is very widely naturalised and often invasive, including in Australia, New Zealand, North America, and other countries in temperate and sub-tropical regions.[1]

Description

It is an annual plant growing to between 5–30 cm tall (most plants growing as weeds of cultivation tend towards the smaller end), with smooth hairless stems. The leaves are oval-acute, 1–3 cm long, with a smooth margin. It has green flowers in three-rayed umbels. The glands, typical of the Euphorbiaceae, are kidney-shaped with long thin horns.[4]

This is Clip Two from on line literature on ingenol mebutate.

Medicinal uses

The plant’s sap is toxic to rapidly replicating human tissue, and has long been used as a traditional remedy for common skin lesions, including cancer.[5] The active ingredient in the sap is a diterpene ester called ingenol mebutate. A pharmaceutical-grade ingenol mebutate gel has approval from the US Food and Drug Administration.In four multicenter, randomized, double-blind studies, we randomly assigned patients with actinic keratoses on the face or scalp or on the trunk or extremities to receive ingenol mebutate or placebo (vehicle), self-applied to a 25-cm2 contiguous field once daily for 3 consecutive days for lesions on the face or scalp or for 2 consecutive days for the trunk or extremities. Complete clearance (primary outcome) was assessed at 57 days, and local reactions were quantitatively measured.

RESULTS
In a pooled analysis of the two trials involving the face and scalp, the rate of complete clearance was higher with ingenol mebutate than with placebo (42.2% vs. 3.7%, P<0.001). Local reactions peaked at day 4, with a mean maximum composite score of 9.1 on the local-skin-response scale (which ranges from 0 to 4 for six types of reaction, yielding a composite score of 0 to 24, with higher numbers indicating more severe reactions), rapidly decreased by day 8, and continued to decrease, approaching baseline scores by day 29. In a pooled analysis of the two trials involving the trunk and extremities, the rate of complete clearance was also higher with ingenol mebutate than with placebo (34.1% vs. 4.7%, P<0.001). Local skin reactions peaked between days 3 and 8 and declined rapidly, approaching baseline by day 29, with a mean maximum score of 6.8. Adverse events were generally mild to moderate in intensity and resolved without sequelae.

CONCLUSIONS
Ingenol mebutate gel applied topically for 2 to 3 days is effective for field treatment of actinic keratoses. (Funded by LEO Pharma; ClinicalTrials.gov numbers, NCT00742391, NCT00916006, NCT00915551, and NCT00942604.)

So there I was with healthy petty spurge plants and the above info.  I started experimenting on the actinic keratosis on my face.