Molecular phylogeny, radiation patterns and evolution of life-history traits in Ursinia (Anthemideae, Asteraceae)

[摘要] Sequence data from the Internal Transcribed Spacer (ITS) of the nuclear ribosomalDNA were used to study the phylogenetic relationships in the genus Ursinia Gaertn.(Asteraceae, Anthemideae) in the southern African region. Closely related genera, i.e.Cotula L., Osteospermum L. and Agoseris Raf., were used as outgroups. The studyalso included maximum parsimony and principal component analyses.The taxa within the genus Ursinia had previously been classified into two subgenera,Ursinia and Sphenogyne R.Br., mainly on the basis of distinct cypsela characters. Themaximum parsimony, principal component and the phylogenetic analyses revealedtwo subgenera, corresponding to the existing subgeneric classification. Principalcomponent analysis shows that the pappus, the number of pappus bristles and thecolour of the cypsela are the most informative characters.However, the low number of phylogenetically informative characters of the ITSsequences, the poor resolution in the consensus tree, and low branch support valuesindicate that the ITS data contain weak phylogenetic signals. The low bootstrap valuesfor many nodes suggest that one should be cautious in using the ITS region alone tomake final conclusions about the origin and evolution of taxa. In maximum parsimonyanalysis, the RI, CI and bootstrap values are low; principal component analysis valuesare also low. Furthermore, there is a lack of resolution in subgenus Sphenogyne. In theliterature, Ursinia is divided into seven series but they were not retrieved asmonophyletic in this study, probably because of short branch lengths in thephylogeny. Further molecular data are therefore required to be able to support orreject the present classification. Maximum parsimony, principal component andmolecular analyses show that U. trifida f. calva Prassler and U. trifida (Thunb.)N.E.Br. f. trifida are not sister taxa, supporting the recognition of these two taxa asseparate species.The Ursinia taxa from the summer-rainfall region are not monophyletic and are sisterto a clade of Cape species. This supports a hypothesis that Ursinia migrated from theCape into the Drakensberg which has been shown for a number of other Cape groupsthat have Drakensberg relatives.

[发布机构] Stellenbosch University