VARIATION IN A POLYPLOID, DIOECIOUS LIVERWORT, MARCHANTIA-GLOBOSA

This study was undertaken in order to determine the population structu re in a tropical, geographically isolated liverwort, Marchantia globos a Brid. ex Web., a thallose species endemic to the Mascarenes and Como ro Islands. A survey of numerous populations on Reunion showed M. glob osa to be ecologically tolerant and morphologically quite variable. Th e morphological differences between populations could only be explaine d by a size effect, due principally to altitude. Neither cytological n or electrophoretic analyses revealed any genetic basis for distinguish ing subpopulations. In spite of an apparently high reproductive effort , sexual structures being produced abundantly, few spores reach maturi ty. No electrophoretically detectable genetic polymorphism was found. Morphological variation appears to result from phenotypic plasticity.