Chemical evidence from the flavonoids relevant to the classification of Malus species

The phenolic compounds of the leaf and bark of Malus species have been examined. The dihydrochalcone phloridzin and a range of flavonoids occur in all barks, but eight compounds were found in only a limited number of species and their distribution shows a relationship with the taxonomy of Malus, providing useful additional characters. The various proposed classifications of Malus species are discussed in the light of this evidence and that of Rehder is found to be in best agreement except for his placing of M. florentina which, by its chemistry, is clearly related to the section Docyniopsis. The geographical distribution of the distinctive phenolics suggests a wide spreading of early Malus probably from south-east Asia as far as North America and a later diversification confined almost entirely to Eurasia. The different phenolic patterns are discussed and related to proposed phytogenies of Malus.