Taxonomic significance of coumarins in species from the subfamily Mutisioideae, Asteraceae

Asteraceae, the largest family of angiosperms, is divided into 12 subfamilies. The Mutisioideae, which has many representatives in southern South America, is divided into three tribes: Mutisieae, Nassauvieae and Onoserideae. The taxon is highlighted by the production of 5-methylcoumarins, compounds that occur in few families of plants. Within Asteraceae, they are almost restricted to representatives of this subfamily. As the substitution patterns of the 5-methylcoumarins vary in the species of the three different tribes, their occurrence may have a taxonomic significance. Most of the 5-methylcoumarins present terpene moieties connected to the coumarin scaffold. Prenyl and geranyl substituted coumarins are predominant in species of Mutisieae, while in those of tribes Onoserideae and Nassauvieae, compounds chiefly present sesquiterpene units attached to C-3 and C-4 of the alpha-pyrone moiety. Another interesting observation is the occurrence of furanocoumarins, restrict to species from the tribe Mutisieae. This type of coumarins is rare in Asteraceae. From a biological point of view, the 5-methylcoumarins have been scantily investigated.