NATURAL AND EXPERIMENTAL HYBRIDIZATION IN POTENTILLA

Abstract

Three natural hybrids have been reported in Potentilla subseries Tormentillae: Potentilla Y. suberecta, P. ×mixta and P. × italica. This paper presents results of morphological and cyto‐logical studies and experimental crosses made to clarify the origins and taxonomy of the hybrids, and to investigate the possibility of introgression. All natural hybrids examined were hexaploid (2n= 42). Experimental crosses confirmed that P. × suberecta is the hybrid between P. erecta (2n= 28) and P. anglica (2n= 56), but the origin of the other hybrids is less clear. It is suggested that the names P. ×mixta and P. ×italica have been applied to different forms of a single variable taxon, and that P. × italica should be regarded as a synonym of P. ×mixta. The origin of this natural hybrid remains uncertain. It is generally considered to be P. reptans (2n= 28) ×P. anglica, but numerous attempts to hybridize these species have failed, although one unpublished, successful hybridization is cited. Experimental crosses have indicated an alternative origin for P. ×mixta, by hybridization between P. reptans and P. erecta, in which the former either contributes an unreduced gamete or occurs as an autopolyploid cytotype. Vigorous backcross progenies were raised from both P. ×suberecta and P. ×mixta and the importance of backcrossing and introgression in natural populations is discussed. Copyright © 1970, Wiley Blackwell. All rights reserved