It is usually not difficult to learn to recognize at least the genera of true aquatic plants in sterile condition. Waterweed (Elodea), wild-celery (Vallisneria), pondweed (Potamogeton), coontail (Ceratophyllum), water-milfoil (Myriophyllum), bladderwort (Utricularia), water-lily (Nymphaea), and others are known, often by name, to fishermen and other outdoorsmen as well as to botanists. Other aquatic plants, such as Subularia and Littorella, may be very rare and of interest from an ecological and phytogeographical standpoint. Still others, although usually emergent, may have truly aquatic forms. Although these plants are reasonably distinctive even when lakcing flowers and fruit (which is usually the condition of many of them), most botanical manuals make their identification difficult by requiring a knowledge of reproductive parts which are at best obscure and more often missing completely. It ought not be necessary to decide first whether duckweed and watermeal (Lemna and Wolffia) are monocots or dicots in order to key them down. Coontail (Ceratophyllum) is absolutely distinctive even if one does not know the nature of the perianth (or, worse yet, the placentation, upon which many keys depend). Within the limitations of scope described below, the key which follows should make more easy the identification of true aquatic plants in Michigan (and to a greater or lesser extent, in neighboring areas).