Nymphaeales: Systematics

The Nymphaeales have long been considered a "primitive" group of flowering plants. By primitive, botanists mean that the group evolved and became distinct very early in the evolution of flowering plants -- some time in the Cretaceous. Currently, there is one view that maintains waterlilies are representative of the earliest members of the angiosperms. In this view, the earliest flowering plants were the paleoherbs, a group of small plants that do not produce wood. The alternative view is that the first flowering plants were small woody trees.

In either case, the Nymphaeales are certainly an early group. One line of evidence to support this is that they carry a mix of traits normally not found together in the same plant. Specifically, they have traits of both monocots and dicots, the two groups into which flowering plants may be divided. Apparently, waterlilies evolved before the separation of these two great evolutionary lines. Waterlilies have the stem anatomy of dicots, with an organized ring of vascular tissue, while they have the plastid anatomy of monocots. Some species of the genus Nymphaea even have what looks like a single cotyledon.

The images above illustrate some of the diversity of waterlilies. At left is Nelumbo (lotus); at top right is Nuphar polysepalum; at bottom right is Nymphaea alba; and at center are the unopened blossoms of an unidentified species of Nymphaea growing in the Budapest botanical gardens.

There is no universally accepted classification of all waterlilies, though one popular system divides the living species into four families:

Inclusion of the lotus (Nelumbo) within the waterlilies is somewhat troublesome. Unlike other watelilies, Nelumbo has tricolpate pollen, that is its pollen has three openings instead of the single slit that is found in the pollen of other waterlilies. This may not sound very significant, but in fact tricolpate pollen is otherwise found only among eudicots. Recent molecular studies also place Nelumbo among the eudicots, in a basal group informally known as the "Lower Hamamelidae" that includes sycamore and saxifrage among others.

Family descriptions have been made available for Barclayaceae, Cabombaceae, Nelumbonaceae, and Nymphaeaceae as part of the DELTA Project.

Visit the Tree of Life for current views on the relationships of Nymphaeales.

Image of the Nymphaea from Budapest taken by Brian R. Speer. Other images property of the Jepson Herbarium, and used with permission.

Sources:
M.W.Chase, et al., 1993. Phylogenetics of seed plants: An analysis of nucleotide sequences from the plastid gene rbcL. Ann. Missouri Bot. Gard. 80: 528-580.

S. Magallón, P. R. Crane, & P. S. Herendeen, 1999. Phylogenetic Pattern, Diversity, and Diversification of Eudicots. Ann. Missouri Bot. Gard. 86(2):297- 372.