cleistogamy

The production of flowers that do not open to expose the reproductive organs, so preventing cross pollination. Some species are obligately cleistogamous but others may be cleistoga-mous only under certain climatic conditions, as in Viola where flowers may not open at low temperatures. In some grasses only the lower florets are cleis-togamous. The evolutionary origin of this mechanism is not known. Compare chasmogamy. See also autogamy.