Cytogenetic Studies in the Genus Helianthus L.

II. Karyological studies in twelve species

Abstract

Karyotypes were prepared in twelve species ofHelianthus utilizing root tip metaphase mitoses. Ten species were diploid with 2n=34, H. mollis was diploid with 2n=30 and H. tuberosus was hexaploid with 2n=102. The mean chromosome length between species ranged from 2.2μto 3.5μ, although within a species individual chromosomes could be as small as 1.1μ and as long as 5.2μ. The karyotypes in eight species were presented for the first time and the results in the remaining four species are discussed in view of the earlier published results.
It is concluded that structural changes did not alter the karyotypes to any appreciable degree, since ten of the twelve species were placed in class 2B of Stebbins. Only H. annuus and H. mollis were placed in class 1 B.
Karyotype of H. tuberosus was examined and two of the three genomes taking part in its constitution were tentatively assigned to H. annuus and H. lenticularis.