Barbaloin in aloe species.

Barbaloin levels in the exudates from the leaves of 68 species of ALOE in the Kew collection have been determined by light absorption at 375 nm following separation by HPLC. The exudates from most species contained between 10-20% although a few concentrations of around 30% were found. The level in the leaf was usually around 1% of thedry weight in plants grown in glasshouses at Kew although some species were found to contain up to 5%. The highest concentrations of barbaloin were found in exudates from young mature leaves just below the apex and the level decreased in older leaves towards the base of the plant. Species in the natural groupings of the genus, Section ANGUIALOE and Group 4, all had appreciable concentrations of barbaloin in the leaf exudates. Species containing barbaloinwere distributed throughout the large heterogeneous Sections EUALOE and PACHYDENDRON with no apparent taxonomic significance.