Allopolyploidy in the thalloid liverwort Corsinia (Marchantiales)

The thalloid liverwort Corsinia coriandrina includes morphologically simila r haploid and polyploid populations with an allopatric geographical distrib ution. Haploid and polyploid colonies of the Old World, and one polyploid c olony from Texas have been analysed. The polyploid, monoecious cytotype has a wider geographical range and ecological tolerance than the haploid, dioe cious cytotype which appears to be restricted to southern Europe and Macaro nesia. Similarity coefficients between the two Old World cytotypes based on isozyme data show them to be more genetically divergent than suggested by their morphology, and to fit the definition of sibling species. Fixed heter ozygosity in six of eight enzyme loci suggests an alloploid origin of the O ld World polyploids. The haploid cytotype could be one of the putative pare nts. Alleles in the polyploid that were not detected in the haploid are pre sumably derived from an unknown progenitor. The polyploid New World colony shows significant genetic divergence; it represents a different allopolyplo id sibling species. Accordingly, at least two independent origins of the po lyploid must be supposed; one in the Old World; the other in the New World. The presumed autopolyploid origin of polyploid liverworts is once more cha llenged by our analysis of polyploid Corsinia. Indeed, autopolyploidy has s till not been documented conclusively in any polyploid liverwort.