Patterns of morphological and allelic variation were examined between the two subspecies of Geleznowia verrucosa Turcz. (Rutaceae) and putative hybrids across a rare zone of overlap between the two taxa. Morphometric analyses with 17 quantitative or derived characters differentiated the two subspecies. Individuals within the overlap zone, which were morphologically difficult to characterise, were variously placed indicating their probable mixed parentage. Allelic patterns in 16 allozyme loci were also examined for polymorphism and patterns of distribution. Eight loci were either monomorphic or exhibited low levels of polymorphism. The remaining eight loci and in particular the five aspartate aminotransferase (Aat) loci, strongly indicate asymmetric gene flow and introgression from subsp. formosa ms to subsp. verrucosa ms. In addition, subsp. verrucosa ms exhibited alleles that were unique to this population.