On the origin of plums: A study of sloe, damson, cherry plum, domestic plums and their intermediate forms
In this paper the origin of plums is investigated through a study of intermediate forms of sloe and damson. Furthermore the role of cherry plum in connection with the evolution of plums is discussed, as well as the various opinions on the origin of husbanded and feral damson. There is general agreement that damson is the ancestor of our domestic plums. The cultivation of Prunus insititia since the Neolithic era, as well as the subsequent development and spread of domestic plums, have led to the emergence of several local varieties in both groups.
In order to be informed on the multitude of varieties and range of distribution, the author has collected great numbers of stones of damson varieties and related groups in various parts of Europe and Anatolia. Fruit stones of both damson and domestic plums are shown to have characteristic varietal differences. This study has revealed several morphologically intermediate forms of sloe and damson. The features of these forms indicate that they result from hybridization between sloe and damson, which implies a close relationship between the species.
The conclusions in this study are principally based on results from breeding tests of varieties of damson, sloe, cherry plums and the intermediates, perforrned during the years 1989-1997. The tests demonstrate that fruit stones of black-fruited damson varieties germinate readily and that the seedlings usually develop into normal shrubs or trees. By contrast, fruit stones obtained from damson specimens with yellow, green or red fruits show seed sterility or produces seedlings characterized by poor growth and viability. These features suggest hybridization and such specimens probably originate from crossings between damson and domestic plums. The characteristics found in the progeny of black-fruited damsons suggest that this group represents the original, botanical species.
Fruit stones of cherry plums, irrespective of the colour of the fruits, show high germination capacity while the growth of their seedlings is remarkably homogeneous and vigourous. The strikingly similar features of sloe and black-fruited damsons, the evidence of their close relationship derived from the hybrid forms and the absence of cherry plum features have led to the conclusion that (black-fruited) damson plums developed directly from forms of sloe. The extreme rareness of intermediates between damson and cherry plum and the striking differences in features between these species indicate that cherry plum did not play a role in the ancestry of the damson.