[Basal angiosperms]
Nymphaeaceae
Nymphaeaceae are among the most ancient of angiosperm taxa, along with Amborella. Among the primitive features of the family is that (in Nuphar at least) the endosperm arises from fusion of only 2 nuclei and is therefore diploid, not triploid as in most flowering plants (news link about nuclei; article about who's oldest).
Read about Amborella at The Plant Genome Project; best photo is a cover of Am. J. Bot.
On-line sources
U. Wisconsin Plant Systematics: Nymphaeaceae
Nymphaea in lily pond in Guangzhou, China (photos M. Schefter)
Water lily detail
Lotus is NOT a water lily (Nymphaeaceae) but Nelumbonaceae (Proteales), among the early-diverging eudicots. The carpels are embedded in a large conical receptacle (obvious in the seed heads, below), and the leaves are raised above the water like unbrellas, not floating on it.
Lotus blossom, Guangzhou.
Lotus pond with fruit and flowers