The genus Pellia comprises a group of simple thalloid liverworts, which are distributed throughout the north temperate region of the United States. One proposed species found in this area, P. X appalachiana, is postulated to be a hybrid between P. neesiana and P. epiphylla (Schuster, 1991. J. Hattori Bot. Lab. 70:143-150). In common garden experiments P. X appalachiana shows unreduced fertility. This does not support the hybrid hypothesis. Furthermore, isozyme studies suggest species-specific variation rather than intermediacy in the proposed hybrid. The systematic status of P. X appalachiana should be resolved through comparison of sequence data collected from the internal transcribe spacers (ITS) of nuclear ribosomal DNA from sympatric populations of P. X appalachiana, P. epiphylla and P. neesiana. ITS sequences taken from P. X appalachiana and P. epiphylla show homogeneity to be 73%. However, sequences of ITS regions obtained from several recombinant clones of P. epiphylla siblings suggest the possibility of genomic heterogeneity in the ITS region of this species. It is hypothesized that further ITS data will support the conclusions based on common garden experiments and isozyme gels, which identify P. X appalachiana as a phylogenetically distinct species.

Key words: Pellia epiphylla, Pellia neesiana, internal transcribed spacers(ITS), Pellia X appalachiana