VARIATION IN A POLYPLOID, DIOECIOUS LIVERWORT, MARCHANTIA-GLOBOSA

This study was undertaken in order to determine the population structure in a tropical, geographically isolated liverwort, Marchantia globosa Brid. ex Web., a thallose species endemic to the Mascarenes and Comoro Islands. A survey of numerous populations on Reunion showed M. globosa to be ecologically tolerant and morphologically quite variable. The morphological differences between populations could only be explained by a size effect, due principally to altitude. Neither cytological nor electrophoretic analyses revealed any genetic basis for distinguishing subpopulations. In spite of an apparently high reproductive effort, sexual structures being produced abundantly, few spores reach maturity. No electrophoretically detectable genetic polymorphism was found. Morphological variation appears to result from phenotypic plasticity.