Sesqui-, Di-, and triterpenoids as chemosystematic markers in extant conifers - A review

Chemosystematics is a common tool in systematics and taxonomy of extant plants. Terpenoids have been found to be especially valuable for chemosystematic investigations of conifers. A review of data in the extensive literature revealed some characteristic distribution patterns of sesqui-, di-, and triterpenoids in extant conifer families. The numerous terpenoids can be assigned to approximately 40 sesquiterpenoid, 17 diterpenoid, and only a few triterpenoid structural classes. Some of these terpenoid classes (e.g., cadinanes, humulanes, labdanes, pimaranes) are unspecific and distributed among all conifers. Other structural classes occur in certain clusters of families (e.g., totaranes in Podocarpaceae, Taxodiaceae, and Cupressaceae s.str.) or were restricted to species of only one conifer family (e.g., cuparanes in Cupressaceae s.str.). Cupressaceae s.str. and Taxodiaceae show great similarities in their terpenoid composition (cedranes, thujopsanes) but can be separated by the occurrence of some sesquiterpenoids (cuparanes, widdranes), which were hitherto known only in Cupressaceae s.str. This supports a monophyletic clade of Cupressaceae s.str. within the major Taxodiaceae/Cupressaceae lineage (= Cupressaceae s.l.). Pinaceae differ from the other conifer families because they commonly lack several diterpenoid classes (phenolic abietanes, tetracyclic diterpenoids) and because they contain some distinct sesquiterpenoids (longicyclanes, sativanes), diterpenoids (cembranes), and triterpenoids (serratanes, lanostanes). With the exception of diterpenoid alkaloids (taxanes), Taxaceae contain terpenoids common in the other conifer families. This supports their inclusion as a separate family in the major conifer clade.