Conservation of rare and endangered bryophytes: Input from population genetics

Abstract

Effective conservation of biological diversity, including bryophytes, depends upon adequate knowledge of the genetic structure of natural populations and of the processes that create and maintain genetic diversity. Overall, species of mosses display a range of values for genetic variation similar to that of other land plants, whereas liverworts show lower levels of polymorphism. Within Plagiomnium section Rosulata, levels of variation are lower in rare, narrowly distributed species than in common, widespread taxa. On a more local scale, populations of P. ciliare from disturbed, secondary forests in the Piedmont of the southeastern United States are less polymorphic than those undisturbed, primary forests in the Appalachian Mountains. This may reflect the effects of genetic drift in small, recently recolonized populations. Typically, bryophyte species are more widely distributed than their angiosperm counterparts, yet there is greater genetic differentiation among populations. Genetic differences between species also are much larger, on average, for mosses and liverworths. In some thallose liverworts, disjunct ‘species’ actually consist of a number of genetically highly distinct sibling species. Even in continuously distributed taxa, it appears that gene flow is highly restricted. The small size of bryophytes and their wide ranges, high degree of population differentiation, and low levels of gene flow must all be taken into account in making informed management decisions about rare and endangered bryophytes.