Which one of the following may require pollinators, but is...

Geitonogamy is functionally cross-pollination involving a pollinating agent, genetically it is similar to autogamy since the pollen grains come from the same plant.

Cross pollination involves the transfer of pollen grains from the flower of one plant to the stigma of the flower of another plant. It is also called xenogamy.

Embryo develops from any diploid cell of embryo sac except egg is referred to as apogamy (diploid apogamy).

Some plants never open to ensure complete self-pollination. This condition is called cleistogamy, e.g., Commelina bengalensis, Oxalis, Viola, etc.