Yes, it is a buttercup - Ranunculus.
It is probably one of:
- bulbous buttercup - R. bulbosus - http://en.wikipedia.org/wiki/Ranunculus_bulbosus
- creeping buttercup - R. repens - http://en.wikipedia.org/wiki/Ranunculus_repens
- meadow buttercup - R. acris - http://en.wikipedia.org/wiki/Ranunculus_acris
Closer inspection is needed to decide which (and it could be a species not listed above, or a hybrid).
You should be able to do that yourself now I've given a shortlist and some links as a starting point.
Let us know!
Yes, buttercups are poisonous, but primarily if ingested (secondarily by contact). The nectar and pollen may be safe, at least for pollinators - which would make sense! (Having said that, some species of lime (Tilia) produce flowers that are narcotic to bees.)
There are several things to look for when telling these 3 common buttercups apart - the main ones being leaf shape, flower colour and what the sepals are doing. Bulbous buttercups tend to be on better drained, drier soils and creeping buttercups are in the damper and often more nutrient enriched places.
Creeping buttercups have the most deep golden colour and this is what yoyur plants are. If you look at the sepals (under the petals) you can see that they cup the bottom of the petal - those of the taller, more spindly Meadow Buttercup which has more finely divided leaves are also like this but those of the bulbous buttercup are reflexed, i.e. bent back and folded down against the stem.
Hope that helps
DrFred - Good call. Yes - we can see the sepals are not reflexed, in the last photo.
There are some instructive photos on Debbie Allan's web site:
- http://homepage.ntlworld.com/debbie.allan1/ranunculus_bulbosus.html (reflexed sepals)
- http://homepage.ntlworld.com/debbie.allan1/ranunculus_repens.html (bristly sepals like yours, not reflexed)
- http://commons.wikimedia.org/wiki/File:Ranunculus_acris_flower_back.jpg (sepals not reflexed)
There are some good botanical illustrations here: