Allocation of reproductive resources within inflorescences of Petrocoptis grandiflora (Caryophyllaceae)

Patterns of fruit set were studied in Petrocoptis grandiflora, a species endemic to the northwestern Iberian Peninsula. This plant has a dichasial inflorescence in which the central flower opens first, followed by first-order lateral flowers and then second-order lateral flowers. We investigated whether flowers at different positions in the inflorescence differ in duration, ovule number, nectar production, or probability of fruit set. Our results indicate that mean duration, ovule number, nectar volume, and probability of fruit set are higher for central than for lateral flowers. Fruit set was higher for central than for first-order lateral flowers, and higher for first- than for second-order lateral flowers. To investigate the effects of loss of the central flower, selected inflorescences were manually ''decentred.'' For lateral flowers, analysis of variance indicated that fruit set was affected both by flower position in the inflorescence and by decentring. However, neither total inflorescence fruit set nor mean duration of flowers in the inflorescence differed significantly between decentred and untreated inflorescences. These results suggest that the observed pattern of fruit set in this species is a result of within-inflorescence competition for the limited amount of resources available for fruit production, and that these resources may be redistributed in response to damage to flowers within the inflorescence. Inflorescences of P. grandiflora can thus be considered to act as semi-autonomous units with regard to resource allocation.