Ceratophyllum is a cosmopolitan genus of flowering plants, commonly found in ponds, marshes, and quiet streams in tropical and in temperate regions. They are usually called hornworts, although this name is also used for unrelated plants of the division Anthocerotophyta. Ceratophyllum grows completely submerged, usually, though not always, floating on the surface, and doesn't tolerate drought. The plant stems can reach 1–3 m in length. At intervals along nodes of the stem they produce rin… (More on Ceratophyllaceae)