Distinguishing Nymphaea odorata Ait. from N. tuberosa Paine has been a problem for botanists for many years. Fassett (1940) recognized that some profess difficulty in differentiating these species. Sculthorpe (1967) refers to the Nymphaea odorata complex and to the fact that in Nymphaea there are abundant natural hybrids, most of which are sterile. ... The diagnostic characters generally used in Nymphaea, although many, are sometimes qualitative and thus indistinct. Waterlilies having characteristics of both N. odorata and N. tuberosa are found in many areas. Because of the difficulty indicated by the above statements–and experienced by me in recognizing and separating the species in the UMBS area–a survey of the full range of variations in Nymphaea in this region was begun in 1964. The initial attempt was simply to analyze the N. odorata-N. tuberosa complex as to morphological characters that could be used to separate the species. During the summers of 1965 through 1969, more detailed studies were undertaken, with financial assistance from UMBS and NSF.... The white waterlilies in the Douglas Lake area are a highly variable taxon and there seems to be no good reason for calling them distinct species. They are most certainly a single species or very closely related species that are showing variable responses to their environments.