Interspecific hybridization and the origin of new plant taxa in Scotland

Abstract

Evidence is presented for and against the proposal that two new plant species have originated in Scotland in the very recent past as a result of interspecific hybridization between plants that have colonized 'man-made' habitats. Isozyme and chloroplast DNA evidence has confirmed a recent origin of the new allopolyploid species Welsh groundsel, Senecio cambrensis, in Leith, Edinburgh. Scottish and Welsh forms of the species differ in a number of morphological and life history features, but overall are very similar in morphology. A survey of isozyme variation in what has been considered as another new hybrid species, Epipactis youngiana (Young's helleborine), and its putative parent species, has cast doubt on its supposed origins, i.e. by hybridization between E. helleborine x E. leptochila or E. helleborine x E. phyllanthes and the stabilization of a hybrid product via autogamy. Contrary to expectation, E. youngiana was found to contain a high level of genetic diversity, and a genotypic structure that is indicative of random mating. Moreover, at a Glasgow site it appears to be interbreeding with two of its putative parents, E. helleborine and E. leptochila, to form part of a hybrid swarm. From the isozyme data, it is possible to dismiss the idea that E. phyllanthes may have acted as a parent ofE. youngiana; however, it can not be ruled out that the 'new species' is merely a variant form ofE. helleborine or an introduction rather than a product of hybridization.