Botanical Journal of the Linnean Society, 2007, 154, 79–87. With 21 figures © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society, 2007, 154, 79–87 79 Blackwell Publishing LtdOxford, UKBOJBotanical Journal of the Linnean Society0024-4074© 2007 The Linnean Society of London? 2007 1541 7987 Original Articles KARYOLOGY OF SOROSERIS AND TWO RELATED GENERA J.-W. ZHANG ET AL. *Corresponding author. E-mail: hsun@mail.kib.ac.cn Karyological studies on the Sino-Himalayan endemic Soroseris and two related genera of tribe Lactuceae (Asteraceae) JIAN-WEN ZHANG 1,2 , HANG SUN 1 * and ZE-LONG NIE 1,2 1 Key Laboratory of Biodiversity and Biogeography, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming 650204, Yunnan, China 2 Graduate University of the Chinese Academy of Sciences, Beijing 100049, China Received March 2006; accepted for publication December 2006 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 dip- loids with 2n = 2x = 16 = 14m + 2sm and have a karyotype asymmetry type 1A. Three species of Soroseris are tet- raploid (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 moun- tains and adjacent regions. © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society, 2007, 154, 79–87. ADDITIONAL KEYWORDS: chromosome number – karyotype – Stebbinsia – Syncalathium. INTRODUCTION Soroseris Stebbins is a small genus in the Asteraceae tribe Lactuceae, with six to eight species, established by Stebbins (1940) (see also Stebbins, 1953; Bremer, 1994; Shih, 1997). It is restricted mainly to the alpine mountains of the Himalayan region and south- western China, with three species, Sor. erysimoides (Hand.-Mazz.) C. Shih, Sor. glomerata (Decne.) Steb- bins, and Sor. hookeriana (C.B. Clarke) Stebbins, extending into India, Sikkim, and Nepal. All members of the genus occur in subalpine or alpine thickets, meadows, and scree areas at altitudes ranging from 2800 to 5600 m (Shih, 1997). Soroseris is character- ized by small, entire or pinnatifid leaves, narrow involucres, with four to five inner bracts and florets, the inner bracts becoming spongy-thickened at matu- rity (Stebbins, 1940; Shih, 1997). The placing of Soros- eris within the Lactuceae has been controversial. It was placed in the Crepis subgroup of the Cichorium group by Jeffrey (1966), but Bremer (1994) included it in the subtribe Crepidinae together with the mono- typic genus Stebbinsia Lipschitz. Two species, Sor. chrysocephala C. Shih and Sor. qinghaiensis C. Shih, were transferred to Syncalathium Lipschitz based on their morphological similarity to other mem- bers of that genus (Liu, 1996; Shih, 1997), leaving only six species in Soroseris, as circumscribed by Shih (1997). Stebbinsia was based on Sor. umbrella (Shih, 1997), which Stebbins (1940) had placed in Soroseris sect. Dubyaeopsis. Stebbinsia differs from Soroseris by having large, lyrate-pinnatifid leaves, large involucres with 10–15 inner bracts and 15–40 florets, and by the fact that the inner bracts are not thickened at maturity. Syncalathium, a genus of eight to nine species, occurs mainly in the Qinghai-Tibet Plateau of China