Reproductive Ecology of Dirca palustris L. (Thymelaeaceae)


Bryan J. Peterson

Additional Authors:

William R. Graves


Sept 2011


Dirca palustris

ABSTRACT Prevalence of sexual and asexual reproduction by plants influences genetic and spatial structure of populations. We investigated reproduction in five populations of Dirca palustris that span its distribution from Florida to North Dakota, and identified the contributions of sexual and asexual reproduction to the clustering of individuals that is characteristic of the species. In each population, maximum density of plants was documented by assessing the 10 clusters that appeared most dense. We surveyed these clusters for evidence of recent recruitment, sowed locally collected fruits to estimate potential for germination, and estimated prevalence of clones by using ISSR genetic markers. Maximum density of plants varied markedly among populations, and denser clusters showed evidence of greater recruitment over several years. Germination of seeds one year after fruits were sown varied from 7 to 56% among populations. Genetic analysis, and our observation of cotelydonary scars on young plants, indicate restricted seed dispersal rather than clonal reproduction explains the occurrence of D. palustris in clumps. Plant density and recruitment were greatest in North Dakota, which raises questions about what governs the distribution of D. palustris at this northern and western limit of the species. The population in Florida, where the species is listed as endangered at its southern limit, had the least germination, the greatest extent of granivory, and relatively poor evidence for recent recruitment. D. palustris is rare in the southern portion of its range, and our data demonstrate the population in Florida should be prioritized by conservationists and monitored for recruitment.