The taxonomy of the liverwort genus Porella based on plant morphology has been regarded as difficult. Recent DNA-based studies have brought new insights into the systematics of these liverworts and have uncovered some novel relationships that allowed the resolution of controversial treatments based on morphology. One of the outstanding features of these plants, in addition to their form, is their chemical composition, which is characterized by great diversity of secondary metabolites. In this paper the sesqui- and diterpenoids occurring in Porella species are described and their chemosystematic relevance is explored. On the basis of chemical data, the Porella species have been divided into six chemotypes: the drimane- (I), sacculatane- (II), pinguisane-sacculatane- (III), guaiane-germacrane- (IV), pinguisane- (V) and africane- (VI) types. Species belonging to type I are characterized by their hot taste, whereas the other chemotypes are comprised of non-pungent species. Consideration of recent DNA data shows striking correlations between molecular groups and their terpenoid chemistry. The chemical data suggest that the P. vernicosa complex (chemotype I) deserves recognition as a separate section of Porella and that terpenoids are important chemosystematic markers in the family Porellaceae.
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