Depends how much you like it I guess. It's a fascinating-looking plant and must have its place in the ecosystem. Sounds too toxic if you have children around though. Great pic too.

Yeh they look amazing out on the prairies & meadows and that's where I think they should stay. As mentioned above, they must have their place. Amazingly, many of these 'toxic' plants are later found to have incredible medicinal properties. Great Photo!

This wasn't in my wild flower books so asked Google which says it is Finnish and an annual. So I' have a good look, keep the photo and discard it to be on the safe side in case it seeds.. How did you manage to identify it?

If in doubt and after reading about it I'd get rid...

I knew it was a Ranunculus by the receptacle/flowers so I used my Clapham Tutin and Warburg plant id book no pictures just a botanical key. { had to buy it as essential use/reading for uni; wasn't cheap either}
Once I had a name I found it in my Keeble Martin British flora book, amazing drawings. it is considered a British native. it is found in Northern temperate regions where there is ''shallow water or wet, disturbed, nutrient-rich mud, especially at the edges of ponds, ditches, streams or rivers.'' As mine is a raised brick walled pond it has hitched a lift probably in compost.

http://www.brc.ac.uk/plantatlas/plant/ranunculus-sceleratus

as I don't mind it and wont be rubbing it on myself I will see what it does seed wise. apparently the seeds are long lived. Not seen it in the locality but I've not being looking for it.

Isn't that interesting, just goes to prove the saying that you learn something new every day? If you don't mind it, harbour it, our wild flowers need all the help they can get.