The occurrence of unisexuality and polyploidy in Isotoma fluviatilis

Abstract

In northern New South Wales Isotoma fluviatilis is diploid and hermaphrodite; in southern New South Wales, Victoria, South Australia, and Tasmania it is tetraploid and hermaphrodite; on the coastal plain to the west and north of Sydney it is diploid and dioecious; and near Rylstone (N.S.W.) there occurs one gynodioecious population. The morphology of the different forms is described, and the possibility is discussed that unisexuality and polyploidy in I. Fluviatilis represent alternative mechanisms by which hybridity has been increased in inbreeding marginal populations of diploid hermaphrodites, and that these two mechanisms have been associated with the elaboration of genetic constitutions enabling new territory to be invaded.