I looked into this a few years ago, to trace the origin of the myth. Apparently the myth stems entirely from one case of a child dying of unknown causes in 1911, who had been known to eat poinsettia leaves. There was no other reason, evidential or even documented, to label the plant poisonous for the next 100 years, and I find, when confronted by one of the thousands of Americans still sharing this belief, the best response is to simply pluck a leaf and eat it in front of them.
I looked into this a few years ago, to trace the origin of the myth. Apparently the myth stems entirely from one case of a child dying of unknown causes in 1911, who had been known to eat poinsettia leaves. There was no other reason, evidential or even documented, to label the plant poisonous for the next 100 years, and I find, when confronted by one of the thousands of Americans still sharing this belief, the best response is to simply pluck a leaf and eat it in front of them.