The changes in proportion across Europe of the various sections of apomictic polyploid species of the subgenus Rubus are described. The north western countries have a higher frequency of simple forms of blackberries, whereas south eastern areas, such as the Caucasus and Hungary, have a higher proportion of complex types.
The distributions of the 344 'species' of true blackberries (subgenus Rubus) in Great Britain are analysed collectively for the five sections, from Watson’s data. The centre of diversity is in south east England; this may be related to the proximity with the Continent, or to greater numbers of botanists in this area. The general pattern of distribution appears to reflect the limits of glaciation, with the diversity of species north of the original limits of glaciation falling off very rapidly. The relation between taxonomy and scarcity indicates that the sections with the simpler types are less restricted in their distribution than the sections of complex forms. The relative abundance of Rubus species in Great Britain is analysed, and the number of species plotted against the vice-comital frequency shows a log series. The number of species per vice-county grouped in geometric x 3 classes shows a close fit with the theoretical Poisson distribution.
The basis for the variation in these apomictic polyploid Rubi is considered in relation to the cytological origin of the apomictic mechanism.