CYTOTAXONOMIC VARIATION IN POTENTILLA FRUTICOSA L.

Summary

Potentilla fruticosa is a widespread species for which chromosome numbers of 2n = 14 (diploid), 2n= 28 (tetraploid) and 2n = 42 (hexaploid) have been published from wild populations. These are listed together with a number of new counts. A morphological study of North American and European plants shows that the diploids are hermaphrodite and the tetraploids dioecious, and that the diploids have smaller pollen and stomata than the tetraploids. These distinguishing characters are used to show that the populations of P. fruticosa from northern Europe are tetraploid and those from southern Europe, western Asia and North America are diploid. Subspecific status is given to the tetraploids and diploids; the tetraploid cytotype is the type subspecies and the diploid is named ssp. floribunda (Pursh) Elkington.

It is suggested that the centre of evolution of shrubby Potentillas is in eastern Asia and that westwards migration took place separately to the north and south by tetraploids and diploids respectively. The North American populations are most likely to have immigrated across the Bering Straits from north-east Asia.