Genetic structure and sexual reproductive potential of the perennial aroid Arisaema dracontium

Arisaema dracontium is an aroid perennial herb which grows in wooded floodplains. It occurs throughout a large part of eastern North America, but is considered rare at the northern periphery of its range which includes Canada and a number of northeastern states in the USA. The genetic structure, fertility and fecundity of A. dracontium was studied across the species' range in order to assess whether those aspects of the population biology leave the species more vulnerable in the northern ecological margins.;The study of genetic structure was preceded by an analysis of the mode of inheritance of the species in order to correctly interpret isozyme banding patterns. Existing evidence from chromosome counts and morphology suggest that A. dracontium is diploid in parts of Florida and an autotetraploid throughout the rest of its range. The mode of inheritance was investigated by examining banding patterns from cellulose acetate allozyme electrophoresis. Unbalanced heterozygotes and tri-allelic loci were observed in tetraploid cytotypes; however, only balanced heterozygotes and di-allelic loci were observed in diploid cytotypes. This is consistent with disomic and tetrasomic inheritance, respectively, and also supports the hypothesis that tetraploid cytotypes are autotetraploid in nature.;A survey of allozyme variation revealed that genic and clonal diversity is high in all parts of the species' range although population differentiation and the number of unique twelve-locus allelomorphs was higher in the northern periphery. A single Florida population was sampled, and found to be markedly distinct from all the other populations.;Fertility and fecundity were extremely variable in all regions of the range. Fertility was not lower in the northern marginal areas, however, highly fecund populations had significantly lower seed mass and somewhat lower seed set in the northern margins relative to populations elsewhere in the species' range.