AOBPreview originally published online on January 11, 2007
Annals of Botany 2007 99(2):311-322; doi:10.1093/aob/mcl259
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Phylogenetic Origins of the Himalayan Endemic Dolomiaea, Diplazoptilon and Xanthopappus (Asteraceae: Cardueae) Based on Three DNA Regions
1 Key Laboratory of Qinghai–Tibetan Plateau Ecological Adaptation, Northwest Plateau Institute of Biology, Chinese Academy of Sciences, Xining 810008, Qinghai, China
2 Graduate School of Chinese Academy of Sciences, Beijing 100039, China
3 Key Laboratory of Arid and Grassland Ecology, Lanzhou University, Lanzhou 730000, Gansu, China
4 Faculty of Geography, University of Marburg, Deutschhaustr. 10, D-35032 Marburg, Germany
* For correspondence. E-mail Liujq{at}nwipb.ac.cn or ljqdxy{at}public.xn.qh.cn
Received: 10 April 2006 Returned for revision: 4 July 2006 Accepted: 17 October 2006 Published electronically: 11 January 2007
BACKGROUND AND AIMS: It is an enduring question as to the mechanisms leading to the high diversity and the processes producing endemics with unusual morphologies in the Himalayan alpine region. In the present study, the phylogenetic relationships and origins of three such endemic genera were analysed, Dolomiaea, Diplazoptilon and Xanthopappus, all in the tribe Cardueae of Asteraceae.
METHODS: The nuclear rDNA internal transcribed spacer (ITS) and plastid trnL-F and psbA-trnH regions of these three genera were sequenced. The same regions for other related genera in Cardueae were also sequenced or downloaded from GenBank. Phylogenetic trees were constructed from individual and combined data sets of the three types of sequences using maximum parsimony, maximum likelihood and Bayesian analyses.
KEY RESULTS: The phylogenetic tree obtained allowed earlier hypotheses concerning the relationships of these three endemic genera based on gross morphology to be rejected. Frolovia and Saussurea costus were deeply nested within Dolomiaea, and the strong statistical support for the Dolomiaea–Frolovia clade suggested that circumscription of Dolomiaea should be more broadly redefined. Diplazoptilon was resolved as sister to Himalaiella, and these two together are sister to Lipschitziella. The clade comprising these three genera is sister to Jurinea, and together these four genera are sister to the Dolomiaea–Frolovia clade. Xanthopappus, previously hypothesized to be closely related to Carduus, was found to be nested within a well-supported but not fully resolved Onopordum group with Alfredia, Ancathia, Lamyropappus, Olgaea, Synurus and Syreitschikovia, rather than the Carduus group. The crude dating based on ITS sequence divergence revealed that the divergence time of Dolomiaea–Frolovia from its sister group probably occurred 13·6–12·2 million years ago (Ma), and the divergence times of the other two genera, Xanthopappus and Diplazoptilon, from their close relatives around 5·7–4·7 Ma and 2·0–1·6 Ma, respectively.
CONCLUSIONS: The findings provide an improved understanding of the intergeneric relationships in Cardueae. The crude calibration of lineages indicates that the uplifts of the Qiinghai–Tibetan Plateau since the Miocene might have served as a continuous stimulus for the production of these morphologically aberrant endemic elements of the Himalayan flora.
Key words: Cardueae, Dolomiaea, Diplazoptilon, Xanthopappus, Himalayas, origin, phylogeny, taxonomy
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