Cytological Studies on Some Members of the Family Pontederiaceae

Abstract

Four species under two genera of the family Pontederiaceae have been investigated, namely, Eichhornia crassipes, Solms. (2n=32, n=16), Monochoria hastaefolia, Presl. (2n=28, n=14), M. vaginalis, Presl. (2n=1 52, II 26, III 80, n=III 40), M. vaginalis, Presl. var. plantaginea, Solms.-Laubch. (2n=52). In Eichhornia crassipes 2n=32 chromosomes and n=16 bivalents have been observed in different populations of this species. Such a regular constancy in chromosome number in a species with extensive vegetative propagation is quite remarkable. The evidences so far obtained indicate that polyploidy, aneuploidy and structural changes of chromosomes have played effective roles in the evolution of species of Monochoria. The study of the two genera shows that even though n=16 is deep seated for Eichhornia and n=13 or 14 for Monochoria the two genera certainly represent a natural assemblage under Pontederiaceae as suggested by the taxonomists. This is principally shown by their karyotypes which have remarkable similarities in the gross morphology with each other.