The genus Arnica (Asteraceae) was investigated for phylogenetic relationships and sesquiterpene lactone (STL) content with the aims to trace the evolutionary history of the genus and to investigate possible congruencies between DNA sequence data, secondary chemistry, and biological activity.
Complex evolutionary patterns in Arnica are evident from phylogenetic analyses of chloroplast regions (the rpl16 and rps16 introns and the psbA–trnH, ycf4–cemA, and trnT–L spacers), nuclear ribosomal regions (the internal and external transcribed spacers) and the nuclear low-copy DNA region coding for the second largest subunit of RNA polymerase II (RPB2) between exons 17 and 23. Polymorphism was detected in nuclear ribosomal and low-copy regions, likely caused by polyploidy and agamospermy. Lineage sorting and/or hybridization is a possible explanation for incongruencies between topologies of the different DNA regions. None of the five subgenera in Arnica constitute a monophyletic group according to any of our analyses.
Sesquiterpene lactone profiles were compared to nuclear ribosomal DNA data using phylogenetic inference and principal component analysis for 33 accessions of 16 species. Clusters supported by both STL chemistry and ribosomal DNA sequence data consist of multiple accessions of the same species (e.g. A montana and A. longifolia), indicating that these species are well defined both genetically and chemically, based on our sampling. Support for subspecies classification of A. chamissonis and A. parryi was found in chemical data. For the first time STLs are reported from subtribe Madiinae, sister to Arniciinae.
Anti-inflammatory properties, as measured by inhibition of human neutrophil elastase release from neutrophils and inhibition of the binding of transcription factor NF-κB to DNA, were investigated for extracts of 12 Arnica species. Arnica montana, A. chamissonis and A. longifolia accessions show high inhibitory effects in both bioassays. Generally, species with a more diverse STL chemistry also possess the strongest inhibitory activity in the bioassays.