KARYOTYPIC RELATIONSHIPS AMONG SOME ROSA SPECIES

Mitotic chromosome numbers and measurements were determined for fiftee n species of Rosa, subgenera Hulthemia, Platyrhodon, Hesperhodos, and Rosa (the latter represented by sections Pimpinellifoliae, Carolinae, Cinnamoneae, Synstylae, Banksianae, Chinenses, Caninae, Laevigatae, an d Bracteatae). ALI were 2n = 2x = 14, 2n = 4x = 28, or 2n = 5x = 35, a s expected from previously published chromosome counts. Similar chromo somes were matched in pairs by least-squares analysis of chromosome ar m lengths. Arm ratio and heterogeneity in chromosome length were used to compare these karyotypes among species, sections, and subgenera. Al though the karyotypes were largely symmetric on the basis of both crit eria, homogeneity was greater within sections, and a phenogram was obt ained on the basis of cluster analysis. The subgenera Hulthemia and Pl atyrhodon respectively lay near sections Bracteatae and Carolinae in s ubgenus Rosa, but the convergent evolution of these largely symmetric karyotypes has not been critically assessed on the basis of other, esp ecially molecular, characteristics.