Karyotypic relationships among someRosaspecies

Abstract

SUMMARYMitotic chromosome numbers and measurements were determined for fifteen species of Rosa, subgenera Hulthemia, Platyrhodon, Hesperhodos, and Rosa (the latter represented by sections Pimpinellifoliae, Carolinae, Cinnamoneae, Synstylae, Banksianae, Chinenses, Caninae, Laevigatae, and Bracteatae). All were 2n = 2x = 14, 2n = 4x = 28, or 2n = 5x = 35, as expected from previously published chromosome counts. Similar chromosomes were matched in pairs by least-squares analysis of chromosome arm lengths. Arm ratio and heterogeneity in chromosome length were used to compare these karyotypes among species, sections, and subgenera. Although the karyotypes were largely symmetric on the basis of both criteria, homogeneity was greater within sections, and a phenogram was obtained on the basis of cluster analysis. The subgenera Hulthemia and Platyrhodon respectively lay near sections Bracteatae and Carolinae in subgenus Rosa, but the convergent evolution of these largely symmetric karyotypes has not been critically assessed on the basis of other, especially molecular, characteristics.