Architectural constraint in fruit production of Crotalaria spectabilis (Fabaceae)

We tested the relative influences of plant architecture and whole plant resources as mechanisms for setting flower and fruit production in Crotalaria spectabilis Roth. (Fabaceae). We also examined the effects of plant architecture and competition between flowers and whether low probability of female function in late flowers was associated with an increased allocation to male function. In control plants, we found a significant relationship between the cross-sectional area of a stem supplying an inflorescence and the number of flowers and fruits produced. Furthermore, the location of successful fruit production was non-random and heavily biased to early opening flowers. In contrast, we found no evidence that fruit to flower ratios in C. spectabilis were altered as a result of environmental resources. The removal of early opening flowers was associated with fruit production in later opening ones, indicating that the capability of producing fruits did not differ between flowers, independent of their time of opening. In conjunction with non-random transition probabilities, allocation to male function was greater in later opening flowers than in early opening ones. Taken together, our results support the hypothesis that plant architectural limitations and inflorescence developmental ontogeny are principal determinants of how many fruits will be produced and where fruit production will occur, and that these factors influence sex allocation between flowers within inflorescences.