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.
Comment: "Small" is ambiguous. For details on "Small rivers" (e.g. the Salween river) see http://worldwildlife.org/biomes/small-river-ecosystems. This class will be replaced with a less ambiguous class.