cleistogamous flowers do not open at all, and their anthers and stigma lie in close proximity . Consequently, when the anthers dehisce, the pollen grains come into contact with the stigma of the same flower, making these flowers invariably autogamous . In contrast, chasmogamous flowers are open and rarely achieve complete autogamy, while geitonogamy and xenogamy involve the transfer of pollen between different flowers or plants .