n.1. Any of several small green nonvascular plants of the division Anthocerotophyta, having a flat thallus from which elongated, hornlike spore-producing structures grow.
2. Any of several aquatic vascular plants of the genus Ceratophyllum, forming branched masses in quiet water and having minute unisexual flowers and stiff, forked, whorled leaves resembling antlers or horns.