Strong incongruence between the ITs phylogeny and generic delimitation in the Nemosenecio-Sinosenecio-Tephroseris assemblage (Asteraceae: Senecioneae)

The three genera Sinosenecio, Nemosenecio and Tephroseris form a closely knit group nested in the subtribe Tussilagininae of the tribe Senecioneae (Asteraceae). The generic limits in this assemblage remain unclear and need revision. In this study, we analysed sequences of the internal transcribed spacer (ITS) region of nuclear ribosomal DNA available from GenBank and sequenced 19 accessions of an additional 13 species encompassing all three genera. Phylogenetic analyses based on the ITS variation of 27 species in this assemblage and seven species from related genera of the Tussilagininae suggested that neither Sinosenecio nor Tephroseris is monophyletic. The sampled species of Sinosenecio were scattered in different clades or subclades of the phylogenetic tree. Four species of this genus, including the generic type species (S. eriopodus, S. hederifolius, S. homogyniphyllus and S. subcoriaceus) are clustered in a tentative clade with genera such as Ligularia, Cremanthodium, Parasenecio, Farfugium and Tussilago. The remaining ten Sinosenecio species comprise a highly supported clade together with 13 Tephroseris species and four Nemosenecio species. Within this clade, 10 Tephroseris species together with two Sinosenecio species (S. newcombei and S. koreanus) comprise a monophyletic subclade while the remaining 11 species from all of three genera are clustered into another clade with moderate statistical support. Within the latter subclade, T. changii was revealed to be closely related to four Sinosenecio species, and three Nemosenecio species comprising a monophyletic lineage. These two lineages form a polytomous radiation with the other two Sinosenecio lineages. The generic delimitations of the three genera clearly need some adjustments, which is also supported by previous studies of gross and floral morphology. Two Sinosenecio species (S. newcombei and S. koreanus) should be transferred to Tephroseris, and the genus Sinosenecio should be re-circumscribed to contain those species clustered in the Ligularia-Tussilago clade. Most of the other described species under Sinosenecio and T. changii should either be transferred to an enlarged Nemosenecio concept, or a new genus needs to be established to encompass them. However, the morphological distinctions between these genera require further investigation.

Duke Scholars

Author Liuyang Wang Molecular Genetics and Microbiology