The Population Biology and Demography of Cimicifuga rubifolia Kearney and the Genetic Relationships Among North American Cimicifuga Species

In this beginning study of the population biology of Cimicifuga species, the life history and demography of the long-lived herbaceous perennial, Cimicifuga rubifolia Kearney, were investigated, the genetic structure of some of its populations was studied, and an investigation of the genetic relationships among the North American species was begun.

The life history and demography were monitored in two populations, one of approximately 1400 individuals (1987-1990) and the second of about 400 individuals (1988-1990). A model of leaf area was used to determine the leaf area (photosynthetic size) of individuals and this was followed during the study. Relationships between the leaf area of the individuals and flowering, fruit set, mortality, dormancy and size change were investigated. The population size structures were considered using size class transition matrices. Population genetic structure from throughout the range of Cimicifug rubifolia was assayed using starch gel electrophoresis, and the genetic relationships of the North American Cimicifuga species were studied using electrophoretic methods.

Leaf area was positively related to the ability to flower and set seed while mortality and dormancy were negatively related to leaf area. Reproduction was primarily sexual, with asexual reproduction by rhizome fragmentation occurring rarely. Several plant responses thought to be related to the low precipitation amounts during 1987 and 1988 were noted. The mean size of the plants in both populations increased by approximately 30 percent during the study and the size at which the probability of flowering reached 50 percent varied. Size structure based on size transition probabilities, was not constant. Plant dormancy was frequent and the number of seedlings noted yearly varied widely.

Seven loci were assayed electrophoretically in C. rubifolia. Accumulated gene differences per locus, as measured by genetic distance among populations was insubstantial but, genetic divergence among the populations is indicated by large F_ST values (.197-.468). This appears to be due to reproductive isolation of populations, indicated by high total fixation indices. Gene flow within populations seems to be limited. The ten loci assayed in 6 North American species of Cimicifuga showed the mean genetic identity from pairwise comparisons of the species to be .543. Mean G_ST values ranged from .086 to .503 and seem to be related, in part, to varying breeding systems among the species.