Intergeneric Hybridization between Conimitella williamsii and Mitella stauropetala (Saxifragaceae)

Based on morphology, intergeneric hybridization appeared evident between Conimi- tella williamsii and Mitella stauropetala in a mixed population of these species from western Wyoming. Evidence from starch gel electrophoresis confirmed the occurrence of natural intergeneric hybrid- ization between these taxa. Conimitella williamsii and M. stauropetala each possess unique allozymes at four of 18 loci examined. Using these allozymes as markers, plants of intermediate morphology were determined to be of hybrid origin. Electrophoretic data also suggest that several additional plants were the result of backcrossing of F1 hybrid plants to M. stauropetala, or that they are F2 or later generation plants. Although this is the first report of intergeneric hybridization between Conimitella and Mitella, naturally occurring hybrids have been reported between other related gen- era of tribe Saxifrageae, including Mitella and Tiarella, and Tellima and Tolmiea. The occurrence of hybrids between so many genera of Saxifrageae suggests that barriers to crossability often are not well-developed among genera of this tribe. Furthermore, since these genera are vegetatively very homogeneous and differ largely in floral morphology, the occurrence of intergeneric hybrids sug- gests that they may not be highly differentiated genetically.