The most important phloroglucinol derivatives ("filicins") isolated from rhizomes of Dryopteris species are discussed. The chemical analysis of Dryopteris rhizomes can (in conjunction with classical and cytological methods) provide valuable criteria for the solution of taxonomical problems, particularly as follows: 1. Identification of otherwise uncertain herbarium specimens. 2. Classification of critical taxa in a difficult complex. 3. Understanding of natural relations, including parents in hybrids and ancestors in allopolypoid species. Analytical methods are critically evaluated.
