Najas (Waternymph) is a genus of herb in the family Hydrocharitaceae. They are native to Canada, The Contiguous United States, Puerto Rico, Alaska, and Eastern North America. They have unisexual flowers.
Definition: in which either the stamens or the carpels are missing, vestigial or otherwise non-functional. Each flower is either "staminate" (having only functional stamens) and thus "male", or "carpellate" (or "pistillate") (having only functional carpels) and thus "female". If separate staminate and carpellate flowers are always found on the same plant, the species is called monoecious. If separate staminate and carpellate flowers are always found on different plants, the species is called dioecious.