THE LEAFY LIVERWORT PORELLA-BAUERI (PORELLACEAE) IS AN ALLOPOLYPLOID

Porella platyphylla and P. cordaeana are genetically well differentiat ed in Europe (I=0.486). Isozyme data from 156 European colonies reveal that P, baueri is polyploid and could be an interspecific hybrid betw een these two species. It is characterized by large lobe cells, toothe d margins of the female bracts, and ciliate perianth mouth. Correspond ence analysis using morphological characters revealed that its colonie s cluster into two geographically separated groups, similar to one or other of the putative parental species. These results agree with the g enetic analysis, that also revealed two main allelic associations, eac h with a distinct geographical range. We hypothesize that this pattern was produced by introgression subsequent to hybridization, or by gene silencing. The discovery of this new, allopolyploid species suggests that hybridization is an important evolutionary process in liverworts.