Rosaceae chemotaxonomy and the origins of the Pomoideae

The results of a chemotaxonomic survey of the Rosaceae for the occurrence of flavone C-g!ycosides, together with a general literature review of Rosaceae chemotaxonomy, are compared with the hypotheses of classical botanical taxonomy relating to the origins and evolution of the subfamilies of the Rosaceae. A tentative phyiogenetic scheme is presented, based upon all available taxonomic evidence. The chemotaxonomic data is consistent with the hypothesis that the Pomoideae are of allopolyploid origin, produced by ancient hybridization between primitive forms of the subfamilies Prunoideae and Spiraeoideae, although the possibility cannot completely be excluded that primitive Spiraeoideae only were involved. Flavone C-glycosides, hitherto thought to be restricted in the Rosaceae to Crataegus, have also been detected in the following genera: Pyracantha, Osteomeles, Aronia, Hesperomeles, Malacomeles, Chamaemetes, Dichotomanthes (Pomoideae); Quillafa (Spiraeoideae); Agrimonia, Adenostoma, doubtful traces in Sanguisorba, Potentilla, Alchemilla (Rosoideae). None could be detected in the Prunoideae. The chemotaxonomic evidence supports the hypothesis that Quillaja is a relict of an apocarpous ancestor of the Pomoideae and that Dichotomanthes is a relict of the primitive Pomoideae.