Abstract
Echinochloa crus-galli and E. colonum are widely distributed hexaploid species, and differ from each other in their genomic constitutions. Tetraploid species E. oryzicola is frequently found in paddy fields as a weed mainly in north-east Asia, and is recognized cytologically as a possible tetraploid progenitor of E. crus-galli. Tetraploid strain of E. haploclada used in this study cannot be a tetraploid progenitor of E. colonum, but shows a fair amount of chromosome pairing at nearly the same degree in the F1 hybrids with E. crus-galli, E. colonum and E. oryzicola. This cytological evidence and occurrence of diploid strains of E. pyramidalis and E. haploclada in Kenya and Tanganyika respectively, indicate that tropical East Africa might be one of the presumable centres of origin of the genus.
