petty spurge euphorbia peplus
As a new member with I guess many more questions then answers I can hope to help with this. I had another unidentified plant in my patio garden, looked pretty and I untangled some leaves and within days had a very nasty rash up both my arms and a purple rash across my middle. It took antibiotics, steroids and weeks to clear up. Found out it was the above named plant. I have also since found out that it is being cultivated due to an enzyme it contains which seems so far to target cancer cells in the body.
Good comes from bad, but watch out for the plant.