Abstract: The present paper reports the karyotypes of six species in the family Nymphaeaceae (sensu lato), and discusses its taxonomic position. Results of the karyotype analysis are as follows: (1) Nelumbo nucifera Gaertn. was found to have the karyotype 2n = 16 = 9sm +4m + 3st, which belongs to 2B type. There was one heterozygous pair and one pair of large subterminal chromosomes in the complement. (2) Victoria cruziana Orbign. was shown to have the karyotype 2n= 24 = 8sm+8m+ 8T, which belongs to 2A type. The chromosomes were the largest in the Nymphaeaceae. (3) Nymphaea stellata Willd. wag of 2n =28. No. 1 chromosome possessed two satellites. The chromosomes were the smallest in the Nymphaeaceae. (4) Nuphar pumilum (Timm.) DC. had the karyotype 2n=34=18m 4+16sm, which belongs to 2A type. One satellite was on No. 8 chromosome and the other was easily detached (5) Euryale fero Salisb. ex Konig et Sims. was of 2n=58. The 58 chromosomes were in 29 pairs. Its chromosomes were small. No. 1 chromosome possessed two satellites. (6) Brasenia schreberi J. F. Gmel. was shown to have 2n=72. The 72 chromosomes were in 36 pairs, which could be classified into 4 pairs of large chromosomes. 12 pairs of medium-sized ones and 20 pairs of small ones. Three satellites could be seen in some karyotypes. Except N. nucifera, the karyotypes of all the species are first reported. The great differences in the karyotype and morphological characteristics between Nelumbo and the other members of the Nymphaeaceae suggest that the Nymphaeaceae (sensu lato) be divided into two separate orders, namely Nelumbonales and Nymphaeales. Nelumbonales contains a single family Nelumbonaceae and a monotypic genus Nelumbo, while the other plants belonging to the Nymphaeaceae which constitute the order Nymphaeales. Nymphaeales may also be divided into two separate families, Cabombaceae and Nymphaeaceae. Cabombaceae containing Brasenia and other genera is the most primitive in the Nymphaeales. Nymphaea,Euryale, Victoria and Nuphar are included in the Nymphaeaceae.

Key words: Chromosome, Karyotype, Nymphaeaceae