Abstract
The cytology of two taxa of Pontederiaceae is reported, viz. M. vaginalis (n=26, 2n=52) and M. vaginalis var. plantaginea (n=12, 2n=24). The chromosome number of the latter taxon is a new count. The karyotype of M. vaginalis consisted of three pairs of M type, 7m type, 12sm type and 4 st type with 2B type of asymmetry. In M. vaginalis var. plantaginea, the karyotype consisted of 2 pairs of M type, 5m type, 4sm type and one st type with 2B type of asymmetry. These two taxa show the basic numbers 13 and 6 respectively. They are morphologically almost distinct with conspicuous differences in leaf-shape and plant size. The similarity in chromosome morphology shows their colse relationship. It is suggested that M. vaginalis is an allotetraploid of M. vaginalis var. plantaginea and M. hastaefolia.
