The use of multivariate analysis of karyotypes to determine relationships between species of Opuntia (Cactaceae).
Somatic chromosomes were studied from roots from seven species and two varieties of the genus Opuntia collected from different localities in Eastern India. A chromosome number of 2n=22 were observed in four, 2n=44 in two and 2n=55 chromosomes in one population. The total chromosome length is greatest in O. ficus-indica (2n=55) and least in O. microdasys var. lutea (2n=22). The karyotypes show a similarity in basic number x=11, except for the horticultural variety, O. monacantha variegata with 2n=34. The chromosome sizes range from very small (0.97 µm) to medium (3.46 µm); the primary constriction varies from nearly submedian to median and the numbers of chromosomes with secondary constrictions are from four to six. Numerical analysis of data indicates a general similarity of the karyotypes, with O. ficus-indica occupying a separate position.