Isozyme markers were used to investigate the origin of the polyploid l
iverwort, Pellia borealis (gametophytic n = 18), which was believed to
represent an autopolyploid form of Pellia epiphylla (n = 9). Enzyme v
ariation was studied in four taxa: polyploid P borealis, two recently
discovered sibling species of P. epiphylla complex, and the closely re
lated P. neesiana (n = 9). Gametophytes of the polyploid showed a comp
lex electrophoretic phenotype for three diagnostic enzymes (DIA1, MPI1
and AGO) in contrast to simple pattern in all haploid taxa. It was po
stulated that the pattern found in the polyploid represents a 'fixed h
eterozygous' phenotype resulting from allopolyploidy. Alleles present
in the polyploid were found (with only one exception) in the two sibli
ng species of the P. epiphylla complex, suggesting that they are the p
arents of the allopolyploid. Pellia neesiana was excluded as a donor o
f either of the genomes. Variation in the polyploid suggests at least
three separate origins of P borealis.