Karyological studies on the Sino-Himalayan endemic Soroseris and two related genera of tribe Lactuceae (Asteraceae)

Abstract

Karyological studies were carried out on ten populations comprising six species of Soroseris in the tribe Lactuceae (Asteraceae), all endemic to the alpine Sino-Himalayan region and poorly known cytogenetically. The single species of Stebbinsia (one population) and two species of Syncalathium (three populations) were also examined for the first time. The basic chromosome number for the three genera is x = 8. Stebbinsia and most species of Soroseris are diploids with 2n = 2x = 16 = 14m + 2sm and have a karyotype asymmetry type 1A. Three species of Soroseris are tetraploid (2n = 4x = 32 = 28m + 4sm). A karyotype of 2n = 2x = 16 = 14m(2SAT) + 2sm with type 1A asymmetry was found in Syncalathium kawaguchii, and of 2n = 2x = 16 = 6m + 10sm with type 2A asymmetry for two populations of Syncalathium souliei. The relationships between Soroseris and the other two genera are discussed. Our cytological results suggest that polyploidy plays a minor role in the chromosome evolution of plants from the Himalayan mountains and adjacent regions. © 2007 The Linnean Society of London.