Verticillatum: Answers to key questions leading to this species.

	leaves mostly 8-45 mm long;  NOT [leaves 3-12 (22) mm long]
	flowers in an emersed terminal spike; NOT [flowers in axils of submersed or emersed leaves]
	distal-most flowers in axils of whorled bracts; NOT [distal-most flowers in axils of alternate bracts]
	flower bracts usually more than twice as long as pistillate flowers; NOT [flower bracts usually less than twice as long as pistillate flowers]
	stamens 8; NOT [stamens 4]

Myriophyllum: This family can be distinguished from other Dicotyledoneae aquatic plants as follows: 

	plants growing as long strands; NOT [small tufted plants]
	leaves whorled; NOT [leaves opposite]
	leaves finely dissected; NOT [leaves entire]
	leaves pinnately branched; NOT [leaves dichotomously branched]
	flowers on spikes (except for Myriophyllum pinnatum); NOT [flowers in leaf axils]
	stamens 4 or 8; NOT [stamens 12-16]