Buttercups

A common plant - or weed if they turn up unannounced in your garden - is the Buttercup (Ranunculus repens).

A rather invasive species, it has been introduced to many parts of the world where it is not a native, often with disastrous effects.
There are many species and sub-species(more than 400) in the buttercup family. This one has prostrate runners which creep along the ground, rooting at 'nodes' along it's length and thus spreading.

The flowers are well known to us all as being very shiny. Who hasn't held a picked Buttercup under someones chin, looking for a golden, reflected glow on the skin to 'see if they like butter'? Most buttercups - including this one - are poisonous causing blistering of the mouth. When growing and fresh, they have a very nasty taste, so grazing animals tend to avoid them. However when cut and dried with the mown hay, they lose their poisons and are harmless.