Apium nodiflorum (synonym Helosciadium nodiflorum), commonly called fool's-water-cress, is a flowering plant found in ditches or streams and native to western Europe. It is a low-growing or prostrate perennial with pinnate leaves which have a vague resemblance to those of watercress. Apium nodiflorum has short-stalked umbels of very small white 5-petalled flowers which are opposite the leaves and grow from the side of the stem at the leaf axils. It blooms in Jul (Wikipedia)