A hybridization programme between diploid and tetraploid representatives of the genus Phyllitis has been carried out and two cases of intergeneric hybrids between Phyllitis and species of Asplenium have been synthesized and are described. Chromosome pairing involving tetraploid forms of Phyllitis scolopendrium from both North America and Japan suggests the occurrence of autosyndesis within the tetraploid genomes. This is not encountered in hybrids involving the tetraploid species P. hybrida. An allopolyploid origin for the latter and an autopolyploid origin for the former is probable although the exact parentage is not certainly known in either case. A working hypothesis concerning the possible course of evolution within the group Phyllitis is put forward in conformity with all the evidence, including that from morphology and geographical distribution, and the steps necessary to confirm or refute it are enumerated.