Artificial and Natural Hybridization and Introgression in Rhinanthus (Scrophulariaceae) in Relation to Bumblebee Pollination

Summary Flowers of plants obtained after artificial crosses between Rhinanthus minor L. and R. serotinus (Schönh.) Oborny are compared with flowers in field samples of mixed populations. Hybridization and introgression in different degrees are found to occur in the field. Arguments are given that the occurrence of both is influenced by the behaviour of flower‐visiting bumblebees and their numbers. In the field seed set in open‐pollinated hybrid plants was reduced compared with that of the parents. Variance in seed production is related to hybrid index value in open‐pollinated plants and to stigma position in caged ones. Stigma position is an important character for the direction of hybridization and introgression.