Molecular confirmation of hybrid swarms in the fern genus Polystichum (Dryopteridaceae)

We present molecular evidence for later-generation hybridization between tw o western North American ferns, Polystichum munitum and P. imbricans. Sever al plants in two mixed-species populations were found to have the chloropla stic haplotype of one of the species and the single-locus allozymic genotyp e of the other. Such individuals can only have arisen via matings between F -1 hybrids or by later-generation hybridization. The pattern of morphologic al variation at the two sites is consistent with the molecular data, and to gether the two data sets suggest that the populations are hybrid swarms. Ou r data cofirm the only known case involving temperate-zone pteridophytes wh ere hybridization has gone beyond the F-1 generation at the diploid level.