Lipophilic exudates of Pteridaceae - chemistry and chemotaxonomy

A number of fern species, belonging to several genera of Pteridaceae, exhibit a more or less conspicuous farinose wax, which is mostly located on the lower leaf surface. Production of these waxes is often correlated with the presence of glandular trichomes. Particularly during the past two decades, a series of publications appeared on the chemical composition of these exudates. The major components were found to be flavonoids (chalcones, dihydrochalcones, flavanones, dihydroflavonols, flavones, flavonols), some of them with a complex substitution pattern, including esters and C-methyl derivatives, and even bisflavonoids. Diterpenoids and triterpenoids can also occur in such exudates. It is the purpose of this paper to survey the chemical composition of Pteridaceae exudates and their occurrence within the genera of the family. The chemotaxonomic significance of the flavonoid aglycones at the generic, specific and populational level is briefly discussed.