The Diversity Of Sesquiterpenoids And Their Chemotaxonomic Implications In Ligularia Cass. (Asteraceae)

Sesquiterpenoids are important characteristic compounds in Asteraceae, especially Senecioneae plants. These compounds have been proposed to be potential chemotaxonomic markers, but this application has not been comprehensively investigated. Ligularia Cass. is a large genus of Senecioneae (Asteraceae) and also includes many traditional medicinal plants, whose various types of sesquiterpenoids are their pharmacological active ingredients, which makes the application of sesquiterpenoids as chemotaxonomic markers possible, and having important taxonomic significance and practical meaning.In this paper,535 sesquiterpenoids from 58 species of the genus Ligularia were investigated to assess their taxonomic utility. The presence and absence were encoded as binary taxonomic characteristics and subsequently utilised in a clustering analysis. The previously biosynthesis pathway of sesquiterpenoids was taken into account to explore the relationship among these species contained different sesquiterpenoid types. In addition, the DNA phylogeny and current the morphological taxonomy were also considered to explore the distribution and evolution of sesquiterpenoids in genus Ligularia further. The correlativity between morphological characters and sesquiterpenoid types of the species was also analysed.As a result, eight chemical major sections within the Ligularia were recognised based on the chemical character. Although with several exceptions, the biosynthesis pathway, molecular phylogeny and the morphological taxonomy were found to be related to the chemical sections, which largely confirmed the validity of our chemo-classification for genus Ligularia. Eudesmane might be the relatively primitive chemical character in Ligularia; sesquiterpenoids with eremophilane-skeleton showed a clear evolution process in plants of this genus:eremophilane-12,8-olides and furanoeremophilanes (Ser. Calthifoliae) → furanoeremophilanes (Ser. Retusae) → eremophilane-12,8(14,6)-diolides (Sect. Stenostegia)→ eremophilane-12,8(14,6)-diolides and eremophilane dimers (Ser. Lapathifoliae)→ eremophilane dimers and cacalols (Ser. Racemiferae)→ cacalols and benzofurane-type sesquiterpenes (Sect. Ligularia). Besides, as a result of the SPSS correlation analysis, the plants with pinnate veins of Ligularia often contained eremophilane-12,8(14,6)-diolides and the plants with racemes often contained cacalols.Compared with our previous investigation about the chemotaxonomic implication of sesquiterpenoids in Senecio L., we suggest that the sesquiterpenoid character in Ligularia has some value for the genus taxonomy but should be analysed carefully and critically.