HYBRIDIZATION AND EVOLUTION IN CARDAMINE (BRASSICACEAE) AT URNERBODEN, CENTRAL SWITZERLAND - BIOSYSTEMATIC AND MOLECULAR EVIDENCE

Hybridization between two diploid (2n = 2x = 16) species of Brassicace ae, Cardamine rivalaris and C. amara, at Urnerboden, Central Switzerla nd, resulted in the rather unusual triploid hybrid C. insueta (2n = 3x = 24), and later on in the amphiploid C. schulzii (2n = 6x = 48). The hybrid and the neopolyploid species colonized successfully some manma de biotopes. Plants of C. insueta are mostly functional females with n on-dehiscent anthers, but true hermaphrodite individuals with partly s terile pollen grains also occur within the population. Analyses of cpD NA and nuclear DNA permitted to establish the parentage of the hybrid: the maternal parent which contributed unreduced egg cells proved to b e C. rivularis whereas the normally reduced pollen originated from C. amara. The pronounced genetic variability in C. insueta revealed by is ozyme and RAPD analyses; at variance with the polarized segregation, h eterogamy and strong vegetative reproduction of the hybrid, is possibl y influenced by recurrent formation of C. insueta which party results from backcrosses between C. insueta and C. rivularis but may also proc eed by other pathways. The amphiploid Cardamine schulzii has normally developed anthers but its pollen is sometimes highly sterile. The surp risingly uniform genetic make-up of the new amphiploid species might b e related to its possible monotopic origin and/or young phylogenetic a ge but should be further assessed. Site management seems to be very im portant to a further development of hybridogenous populations and thei r parent species. In conclusion, the evolution at Urnerboden is discus sed in the context of the traditional concept of multiple plant origin s.