Why do flowers close at night? Experiments with the Lesser celandineFicaria vernaHuds (Ranunculaceae)

Although the mechanisms of flower closure have been widely studied, the evolutionary processes underlying this phenomenon are largely unknown. Open flowers may face a trade-off between successful pollination/pollen transfer on the one hand and destruction of reproductive organs caused by exogenous factors (e.g. rain) on the other. The cost of flower opening was investigated by treating flowers of the Lesser celandine both in the field and under laboratory conditions. No differences were found in anthesis and reproductive success between treated and untreated flowers in any of the experiments. However, treated flowers in the field experiment suffered from significantly higher predation rates, in all probability caused by slugs and roe deer. It is suggested that flower closure may decrease the rate of being eaten by some herbivores, particularly in early-spring plants that flower at times of insufficient food availability.