The flowers of ARNICA MOLLIS afforded, in addition to baileyin ( 1A), baileyin acetate ( 1B), xanthalongin ( 3), and 2-deacetoxy-11alpha,13-dihydroxanthuminol ( 6), the new 1,5- CIS-guaianolides arnimollin acetate ( 2A) and arnimollin tiglinate ( 2A) and the new xanthanolides 11beta3,13-dihydroxanthalongin ( 4) and 11alpha,13-dihydroxanthalongin ( 5). No traces of helenanolides were discernible. The structures were elucidated mainly by high-field NMR spectroscopy. The stereochemistry of 1B has been revised on the basis of an X-ray crystallographic study to be a 4alpha,5beta-epoxygermacrolide instead of a 4alpha,5beta-epoxymelampolide. The implications for the biosynthesis of CIS- and TRANS-fused guaianolides are discussed. The co-occurrence of 1A with CIS-fused guaianolides and xanthanolides (no helenanolides) in A. MOLLIS and with TRANS-fused guaianolides and helenanolides (no xanthanolides) in A. ACAULIS supports the hypothesis that germacrolides represent the biogenetic precursors for CIS- and TRANS- fused guaianolides.