The ecological significance of cleistogamy

Sammanfattning: Various aspects of cleistogamy, a reproductive system combining selfing in closed (cleistogamous) flowers and potential outcrossing in open (chasmogamous) flowers, were investigated in four perennial species. The main purpose was to shed some light on the adaptive value of having a dual reproductive strategy, and to test some hypotheses on the maintenance of xenogamy. In field studies including variation between years and sites, chasmogamous (CH) and cleistogamous (CL) flower and seed production were quantified in ramets of different size. Performance of CH and CL offspring under different conditions was examined in comparative field and garden studies, and an experiment on ballistic dispersal of CH and CL seeds was conducted.It was found that in Oxalis acetosella and Viola hirta, CL production is influenced by ramet size and reproductive success in the CH phase. Production in both phases varies considerably among years and sites in O. acetosella, and on the whole reproductive success is not greater in the CL phase than in the CH phase. In addition, the two phases seem to have their optima at different points along temporal and spatial variation scales in O. acetosella. In O. acetosella, Viola mirabilis, and V. riviniana, germination was found to be lower in CL seeds than in CH seeds, and in V. hirta and V. rivinana CL offspring were on average smaller than CH offspring. These differences may be attributable to inbreeding depression in selfed offspring, but regarding seedling survivorship there is no difference between the two offspring types. In the dispersal experiment CL seeds of O. acetosella were thrown farther from the mother plant than were CH seeds, in contrast to data from other species.The results of this study partly contradict the traditional view on cleistogamy and the relationship between xenogamy and autogamy, where perhaps the genetic aspects have been overrated. The main selective value of a dual reproductive system is probably in optimizing individual seed output by compensating for environmental stochasticity.