Since the question of chromosome numbers often comes up but the answers are not available in the popular literature, I thought it would be useful to list numbers for the waterlilies which we grow. Some of these numbers were determined over 70 years ago for waterlily hybrids and cultivars that are no longer found in the trade, but they are included here because they have been described in the literature and used for hybridizing.

First off, the base haploid chromosome number for the genus Nymphaea is x=14.

Because the cells in a flowering plant contain chromosomes originating from the union of two haploid gametes this number is designated as 2n. Consequently, the basic number of chromosomes (2n) in a Nymphaea cell is 2x or 28. The plants with this number are called diploids. However, over the millions of years that the genus Nymphaea has existed on earth, mutations and hybrids have occurred which caused the chromosomes in some cases to increase or decrease in number. When an increase is by whole number factors, these plants are called polyploids. Specifically, when 2n=3x, the plants are called triploids; when 2n=4x, the plants are called tetraploids; when 2n=6x, the plants are called hexaploids, etc., but the champion is our own hexadecaploid N. gigantea with 2n=16x=224. In a few species where the number of chromosomes are not a whole number multiple of the base number x, these are caused by mutations that altered the chromosome numbers by fusion of formerly separate chromosomes or failure of some chromosomes to separate at meiosis. These plants are called aneuploids and are pointed out in the list below.

Hexadecaploid N. gigantea

With this said, it is interesting to note that some waterlily species are found to have more than one chromosome number. This is because although some plants have great variability in their cytological aspects; their physical appearance is not sufficiently different to cause botanists to separate them
into individual species. Historically, chromosome numbers carried no taxonomic weight because the numbers were not available. Variations in chromosome numbers in a single species are most apparent in wide ranging species such as N. alba, N. stellata, and N. lotus. In the mid 1800s when botanist Robert Caspary (member of the Waterlily Hall of Fame) was studying N. alba, he noted nine distinguishable waterlily variations in populations that could be keyed to certain geographical locations. Accordingly, he
assigned varietal names such as Nymphaea alba var.engystigma; West Prussia, near Danzig. His large number of varieties with often modest differences proved too unwieldy for practical use, so Henry Conard (another member of the Waterlily Hall of Fame) only considered the most important variation from the type: N. alba var. rubra (from which all our red hardy waterlilies are derived). Henry Conard's Monograph "The Waterlilies" gives a good summary of Caspary's work in this area. (Note: Betsy Sakata informs me that reprints of this 322 page Monograph are again available at nominal cost to IWGS members.)

The Nymphaea chromosome data was found from the following references:

Gupta, P. P. 1978. Cytology of Nymphaea. Cytologia 43: 477-484

Gupta, P. P. 1980. Evolutionary Trends of the Genus Nymphaea. Cytologia 45: 307-314

Harada, Ititaro. 1952. Chromosome Studies of some Dicotyledonous Water Plants. Jap. Jour. Genet. 27: 117-120

Heslop-Harrison, Yolande. 1955. Nymphaea. J. Ecology 43: 719-734

Langlet, O. & E. Soderberg. 1928. Uber die Chromosomenzahlen einiger Nymphaeaceen. Acta Horti Bergiani 9 (4): 85-104

Wiersema, John H. 1987. A Monograph of Nymphaea Subgenus Hydrocallis. Systemic Botany Monographs 16

Below are the (2n) chromosome numbers for some Nymphaea species in alphabetical order. Note that since these numbers were determined at different periods in the past, that some names may be synonyms depending upon the nomenclature used at the time:

N. alba: 48, 56, 64 Aneuploid, 84, 96 Aneuploid, 105 Aneuploid, 112, 160 Aneuploid
N. amazonum: 18 Aneuploid
N. caerulea: 28
N. candida: ca 112, ca 160 (This may possibly be an aneuploid)
N. capensis: 28
N. capensis var. zanzibariensis: 28
N. gigantea: 224
N. jamesoniana: 28
N. lotus: 28, 56, 84
N. mexicana: 56, 84
N. micrantha: 56
N. odorata: 84
N. oxypetala: 84
N. prolifera: 18 Aneuploid
N. rubra: 56, 84, 112
N. stellata: 28, 56, 84
N. tetragona: 84, 112, 120 Aneuploid
N. tuberosa: 84

Here are the 2n counts for some hybrids:

N. 'August Koch': 28
N. 'Bissetii': 84
N. 'Daubeniana': 42
N. 'Dawn': 56
N. 'General Pershing': 42
N. 'Helvola': 84
N. 'Laydekeri Alba': 56
N. 'Pamela': 42
N. 'Sturteventii': 56
N. 'Sunrise': 84

Additional counts from Dr. John Wiersema's 1987 paper on Nymphaea subgenus Hydrocallis: N. conardii - 2n=28 N. gardneriana - 2n=28 N. lasiophylla - 2n=18 N. lingulata - 2n=18 N. novogranatensis - 2n=28 N. rudgeana - 2n=42? N. tenerinervia - 2n=20

To complete the picture, here are the (2n) chromosome numbers for some other
genera of the Family Nymphaeaceae:

Victoria amazonica: 20
Victoria cruziana: 24
Victoria 'Imperialis Hybrida': 22 (an early hybrid produced by Haage & Schmidt)
Euryale ferox: 58