Why do some orchids pollinate themselves?

In many orchids, self-pollination serves as a vital strategy to avert extinction when conditions are adverse for normal pollination relationships. This often occurs when a plant's customary pollinators are absent from its environment, such as when species colonize new areas where their specific insect partners do not exist.1

Orchids employ several mechanisms to achieve this:

• Averting Sterility: If a flower remains open for a long period without being visited by a pollinator, simple falling of old pollinia can result in self-pollination.1
• Structural Modifications: In some species, the rostellum—the physical barrier that normally separates pollen from the stigma—may degenerate or become stigmatic, allowing the pollen to germinate directly on the stigmatic fluid.1
• Mechanical Movement: Some orchids possess tissues that bend to physically move the pollinia into place on the stigma. One species, Holcoglossum amesianum, even twists its flower 360 degrees against gravity to facilitate self-pollination.2
• Closed Flowers: Certain orchids may not open their flowers at all, ensuring self-pollination occurs internally.1