Turionifera: Answers to key questions leading to this species. 

	Fronds 1-2 times longer than wide, bases rounded, the stalks thin, white, often decaying; colonies smaller, 1-several plants.  NOT [Fronds 2-3.5 times longer than wide, abruptly narrowed to green, persistent stalks 2-20 mm long; colonies 3-50 plants formed from fronds connected by persistent stalks.]
	Plants often forming turions; fronds 1-4 mm long with lower surfaces more intensely red than upper surfaces; papillae mostly distinct on midline of upper surface; seeds with 30-60 indistinct ribs. NOT [Plants lacking distinct turions; fronds 1-8 mm long with lower surfaces less intensely red than upper surfaces; papillae often not distinct; seeds with 8-15 distinct ribs.]

Lemna: Answers to key questions leading to this genus. 

	Roots present, 1-21 per frond; fronds flat or gibbous, air spaces present and veins 1-21; daughter fronds and flowers arise in marginal pouches. NOT [Roots absent; fronds 3-dimensional (globular), without air spaces and without veins; daughter fronds arise from terminal pouches; flowers borne in dorsal cavities on upper frond surface.]
	Roots 1 per frond; fronds green or reddish below, usually narrower but if obovate, then 4 mm long at most; veins difficult to distinguish, usually 3.  NOT [Roots more than 1 per frond; fronds purplish brown below, obovate to circular, up to 10 mm long; veins visible,  7 or more.]

Lemnaceae: Answers to key questions leading to this family. 

Plants free-floating aquatics growing on the surface or suspended in water, solitary and 0.5-15 mm across or attached together in larger colonies; identifiable stems and leaves absent. NOT [Plants larger and with well-defined stems and/or leaves]