The correct option is A Azolla
Azolla is an aquatic fern consisting of a short, branched, floating stem, bearing roots, which hang down in the water. The leaves are alternately arranged and each consists of a thick aerial dorsal lobe containing green chlorophyll and a thin floating ventral lobe of slightly larger size, that is colourless. Under certain conditions, an anthocyanin pigment gives the fern a reddish-brown colour.