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SUMMARY
A cytological survey of a collection of H. rosa-sinensis (x = 9) revealed the following chromosome numbers 2 n=46, 54, 63, 68, 72, 77, 84, 90, 96, 112, 132 and 144. The 12 cytotypes could be divided into two distinct groups, a polyploid group (2 n = 54, 63, 72, 90, 144) and a dysploid group (2 n = 46, 68, 77, 84, 96, 112, 132). In the former, flower diameter was found to be directly proportional to chromosome number, while in the latter it was inconsistent.
The probable mechanism involved in the origin of H. rosa-sinensis complex seems to be intervarietal and interspecific hybridization involving different basic numbers and levels of polyploidy. This together with segretational errors have been responsible for the origin of dysploids. Sexual sterility is very common. This may be genie, chromosomal and environmental but is of no consequence because of the vegetative multiplication.