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