CYTOGENETIC STUDIES OF CARTHAMUS DIVARICATUS WITH ELEVEN PAIRS OF CHROMOSOMES AND ITS RELATIONSHIP TO OTHER CARTHAMUS SPECIES (COMPOSITAE)

Carthamus divaricatus (Beg. et Vacc.) Pamp., found only in Libya, has 11 pairs of chromosomes, a new chromosome number in the genus. The species is distinct morphologically. It has yellow, purple, and white corollas, yellow pollen, dark-purple striped anthers, horizontal branches, and strongly divaricate outer involucral bracts. The terminal portion of the middle involucral bracts is dentate and reddish brown. It is self-incompatible. Meiosis is regular in the different corolla-color types of C. divaricatus and their intraspecific hybrids. C. divaricatus was crossed to six species with n = 12, to three species with n = 10, to C. lanatus with n = 22, and to two species with n = 32 chromosomes. The morphological characteristics and cross-ability of the parental species plus the pollen viability, seed-set, and meiotic behavior of the hybrids involving C. divaricatus and other Carthamus species indicated that C. divaricatus is very closely related to species with n = 10, closely related to C. lanatus with n = 22, and less closely related to C. tinctorius with n = 12 chromosomes. C. divaricatus seems to be distantly related to C. nitidus (n = 12). It is proposed that C. divaricatus be included provisionally with 10-chromosome species in Section II. Alternative hypotheses for the development of the three basic chromosome numbers are discussed.