Relationships and hybridization between British species of Polygala – evidence from isozymes

summary In Britain there are four species of Polygala , three diploids, P. serpyllifolia, P. calcarea and P. amarella , and a tetraploid, P. vulgaris , all of which are morphologically similar. Isozymes of six enzyme systems in these species were compared. Using evidence from both morphology and isozymes, the closest relationship within the group is between P. serpyllifolia and P. vulgaris. Despite this, P. serpyllifolia and P. vulgaris do not hybridize, whereas P. calcarea and P. amarella both hybridize with P. vulgaris in natural populations. In four sites, where P. calcarea and P. vulgaris occur together, there is good evidence for introgression via hybrids of P. calcarea genes into the tetraploid P. vulgaris , despite the high level of sterility in hybrids. Introgression of P. vulgaris genes into P. calcarea might have occurred at one site.