The occurrence and taxonomic distribution of the anthrones aloin, aloinoside and microdontin in Aloe

A chemotaxonomic survey of 380 species of Aloe indicated the presence of th e anthrone isomers aloin A and B together with the aloinoside isomers and m icrodontin A and B in 36 (10%) species of Aloe. This group, referred to as the microdontin chemotype, is thus characterised by a combination of exudat e compounds and not merely a single phytochemical marker, implying taxonomi c significance of leaf exudate compounds. The 36 representatives of the gro up occupy disparate taxonomic positions in the largely artificial hierarchy of the present classification system. Although many of the species have pr eviously been considered as related (based on macromorphology only), a larg e number of species have not been associated with one another before. The c hemical profiles and leaf exudate compositions of the species are presented , followed by a brief summary of the morphological diversity. Whilst conced ing the possibility of convergent evolution, the geographical distribution of the species and thoughts on possible relationships between the taxa are discussed. (C) 2000 Elsevier Science Ltd. All rights reserved.