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Reproductive Biology of Nymphaea (Nymphaeaceae)

1988; Missouri Botanical Garden; Volume: 75; Issue: 3 Linguagem: Inglês

10.2307/2399367

2162-4372

John H. Wiersema,

Botanical Research and Chemistry

Several reproductive strategies have evolved within the genus Nymphaea.Sexual reproduction is mostly protogynous; flowers are open two to several days (depending on the species) , with pollen release usually commencing on the second day.The five subgenera of Nymphaea exhibit differences in floral biology.There is considerable variation in the timi , ing, floral odor, flower color, and the form and Junction of various flower parts.These differences may < <»• olation between species both through temporal separation of flowering and at in i.ollinators.While sexual reproduction in many species is d p nd t xogamy or geilonogamy, other species have adaptations to promote autogamy.No species of Nymphaea is known to be agamospnmous.but several other modes of asexual reproduction are exhibited: detachable tubers, stolon formation, and proliferations of floral and foliar tissue.Wide-ranging tropical species all avoid being totally reliant on pollinators by employing one or more reproductive alternatives to outcrossing; clearly some obligate outcrossers are limited in their colonizing by pollinator availability.The most important of these reproductive alternatives is autogamy.Wide-ranging temperate species, which mostly rely exclusively on outcrossing for sexual reproduction, probably avoid pollinator limitations by utilizing a broader range of \vmphuea is the largest and most widely dis-of these, however, has attained the species radiation tributed genus in the Nymphaeales.About 40 and global species of waterlilies, as they are commonly known, According to Gupta (1978Gupta ( , 1980) ) polyploidy, The classification of Conard (1905), still generally tions have played important roles in the evolution accepted, recognizes five subgenera: the north-tem-of Nymphaea.The poor development of isolating perate subgenus Nymphaea, neotropical subg.//> -mechanisms is also mentioned as being responsible drocallis, and paleotropical subg.Lotos of the syn-for the high incidence of natural arid artificial mcarpous group and the Australian subg.Anecphya terspecific hybridization.However, such mechaand pantropical subg.Brachyceras of the apocar-nisms are not altogether absent.Certainly ecologpous group.The success of this genus as deter-ical factors help isolate certain species from others, mined by number of species and distributional range such as the alkaline-tolerant N. tuberosa Paine is due to several factors.Its age, dating probably from the more acidophilic N. odorata Aiton, or from mid Tertiary (Collinson, 1980), may be one the slightly halophilic N. rudgeana G. Meyer from factor; however, other nymphaeaoid genera of less salt-tolerant species, or the riparian A', potacomparable age have not demonstrated the same mophila Wiersema from lacustrine species.Geodegree of evolutionary divergence.Another factor graphical isolation has also been a factor, such as is its specialized but widely available ecological separating N. alba L. of Europe from the North niche.Waterlilies almost invariably inhabit still or American N. odorata.gently flowing water over rich organic substrates.This paper, in discussing the reproductive bi-In stable aquatic habitats they root in water too ology of Nymphaea, focuses on several potential deep for competing emergent vegetation.Their external mechanisms for reproductive isolation.Infloating leaves, in addition, outcompete submersed ternal mechanisms (terminology from Grant, 1 98 1 ) leaves for light.A few other genera are competitors no doubt are important in promoting the hybrid for this niche, including primarily nymphaeaceous breakdown and sterility often observed in Nymgenera such as Nuphar, Brasenia, and Nelumbo, phaea (Gupta, 1978) but are outside the scope of and the distantly related genus Nymphoides.None this discussion.