Nasturtium officinale

Native to Europe, western and central Asia, parts of Africa, and the Atlantic islands, it is a perennial aquatic or waterside herb. It grows in muddy or gravelly ground beside running water and can float over the surface. Small white flowers have four petals arranged in a cross. The species belongs to the mustard family, Brassicaceae, and is widely known as an edible leafy plant. It has escaped cultivation and become naturalized across much of Japan. Photographed in Colombia.