Cytological relationships between three diploid species of the fern genus Ceratopteris

Abstract

The cytological and reproductive characteristics of synthesized hybrids involving three diploid species of the homosporous fern genus Ceratopteris Brongn. have been examined. Cytological data indicate that the three species have major chromosomal homologies but differ with respect to a few structural rearrangements involving translocations and inversions. All of the hybrids were semi-sterile but F2 generations were obtained in which moderate to full fertility was evident. No relationship was evident between the degrees of morphological similarities between the species and the degrees of cytological and genetic differences expressed in the hybrids. These factors have confused species relationships among the diploid members of the genus. The behavior of the diploid hybrids is unique among the homosporous ferns in that cytological differences between the species involve individual chromosome differences rather than differences or similarities at the genomic level.