Reproductive ecology of a Great Lakes endemic, Cirsium pitcheri.

Abstract

Seed production is important for maintaining population size of species with limited vegetative reproduction. My focus of the study was on the effect of damage to apical meristem during vegetative stages on reproductive output of Cirsium pitcheri, a threatened species endemic to the Great Lakes. Plants that had suffered from apical meristem damage were identified as multistemmed individuals. Probability of flowering as a function of plant size was examined by comparing of flowering and non-flowering adults. Reproductive output was estimated using the average number and the total diameter of flowering heads per plant. The vegetative characteristic best predicted the size of flowering plants was identified, and size difference was eliminated in the analyses that compared reproductive outputs between damaged and undamaged plants. Total seed set and percent seed set in relation to the size of capitulum also was compared between damaged and undamaged plants. Probability of flowering was confirmed to be size-dependent, and taproot diameter was the best size predictor for flowering plants. Total head number and total head diameter produced per plant was not significantly different between damaged and undamaged plants at all four sites in northern Michigan. While total seed set and percent seed set increased proportionally as head size increased, this relationship did not differ significantly between damaged and undamaged plants. Therefore, damage to apical meristem has no negative or positive effect on the reproductive output of Cirsium pitcheri.