Floral Biology And Reproductive Morphology Of The Nymphaeaceae

The Nymphaeales were consistently identified by recent molecular phylogenetic analyses as one of the three earliest lineages of angiosperms (the ANITA clades: Amborellaceae, Nymphaeales, Illiciales, Trimeniaceae, and Austrobaileyaceae), which, together with the new record of fossils of water lily flowers from the Early Cretaceous, support the long-held view that the Nymphaeales represent a primitive taxon. The critical phylogenetic position of the Nymphaeaceae, which belong to the Nymphaeales, has not so far drawn much attention of researchers to the characters of reproductive biology and reproductive morphology that might represent plesiomorphies in the angiosperms evolution. The present studies carefully investigated the floral biology of Victoria, Nuphar and Nymphaea, the embryology of Nuphar microphylla, the pollen morphology of the Nymphaeaceae, the developmental morphology of the ovule and seed of the Nymphaeaceae, the morphology and anatomy of the stigma in the Nymphaeaeceae. The flowers of the Nymphaeaceae studied all show the phenomenon of biological clock. The regular opening and closing movements of the floral organs occur during anthesis. Some species are day-blooming, whilst the others are night-blooming. The flowers are mostly protogynous and they are open two to several days (depending on the species) with pollen release usually commencing on the second day of flowering. The different genera of the Nymphaeaceae exhibit considerable variation in the timing of flower opening, flower odor, flower color, the form and function of various flower parts and the preference of pollinators. Based on my studies on Victoria cruziana, it is suggested that the flowers of Victoria are highly specialized for and adapted to pollination by insects. My investigations on the floral biology of Nuphar microphylla support the contention of Lippok et al. that the relative contribution of flies, bees, and beetles to pollen transfer in any one population depends more on the relative abundance of these insects and alternative food sources than on stamen length differences between the Old World and New World pond lilies. Here I report in Nuphar microphylla a new pattern of four-celled/five-nucleate female gametophyte (with an egg cell, two synergids, and a central cell with two haploid nuclei). I speculate that this type of female gametophyte may be the minimal sexually functional size, and that it is likely to be plesiomorphic for flowering plants. The Nymphaeaceae is an eurypalynous family. Pollen aperture of this family can be divided into two types—anasulcus and zonasulculus. It is suggested that the anasulcate pollen of Nuphar represents the most primitive pollen type in the Nymphaeaceae. The view that the Nymphaeaceae is one of the most primitive angiospermous families is supported by pollen morphology. In all the species of the Nymphaeaceae examined, the inner integument arises as a ring, but the outer integument initiates as a semiannular outgrowth interrupted on the concave side of the funiculus, then the outer integument becomes hood-shaped. The outer integument is hood-shaped at early stages of ovule development, but becomes cup-shaped later in Nymphaea rubra, N. lotos, N. mexicana, Euryale ferox, and Victoria cruziana. It is suggested that the hood-shaped outer integument is primitive and the cup-shaped one is derived in Nymphaeaceae. The family is highly diverse in stigma type. The stigmatic surface in Nymphaea is covered with numerous crowded multicellular papillae. The stigma in Nuphar and Euryale is unicellular-papillate. The stigmatic surface appears bumpy in Victoria. Den Hartog's hypothesis that Ondinea is closely related to Nymphaea is supported bystigma morphology.