Abstract:

The present paper reports the chromosome number and karyotype of the genus

Hydrilla. H. verticillate was found to have 2n=16.  The karyotype is 2n=16=6m+6sm+

4st.  No difference between the male and the female was found in the work. H. verticillata

var. roxburghii Casp. has the somatic chromosome number 2n=24, and its karyotype is 2n=

3x=24=9m+9sm+6st.  The variety may be a autotriploid.   The karyotype of the genus is

obviously bimodal, with No. 1-5 in the first group and 6-8 in the second group.

Key words: Hydrilla verticillata, H.verticillata var.roxburghii, Karyotype