Apium nodiflorum Fool's-water-cress CC DD N
This a plant you often find in overgrown ditches or very damp places. It can be tall but most often it sprawls sending out stems almost at right angles to the main stem. The white flowers (umbels) appear in the axils and individual groups of florets are often widely separated. It is a very common plant in England and Wales but far less common in Scotland. It can be confused with Berula erecta (Lesser water-parsnip) which has a distinct ring on the leaf stalk.
It is very common throughout England, Wales and Ireland but is much less common in Scotland.