Allopolyploidy in the Thalloid Liverwort Corsinia (Marchantiales)

Abstract:The thalloid liverwort Corsinia coriandrina includes morphologically similar haploid and polyploid populations with an allopatric geographical distribution. Haploid and polyploid colonies of the Old World, and one polyploid colony from Texas have been analysed. The polyploid, monoecious cytotype has a wider geographical range and ecological tolerance than the haploid, dioecious cytotype which appears to be restricted to southern Europe and Macaronesia. 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 heterozygosity in six of eight enzyme loci suggests an alloploid origin of the Old World polyploids. The haploid cytotype could be one of the putative parents. Alleles in the polyploid that were not detected in the haploid are presumably derived from an unknown progenitor. The polyploid New World colony shows significant genetic divergence; it represents a different allopolyploid sibling species. Accordingly, at least two independent origins of the polyploid must be supposed; one in the Old World; the other in the New World. The presumed autopolyploid origin of polyploid liverworts is once more challenged by our analysis of polyploid Corsinia. Indeed, autopolyploidy has still not been documented conclusively in any polyploid liverwort.