Which Mechanisms plants use to avoid self-pollination in bisexual flowers

Although bisexual flowers contain both reproductive organs, plants have evolved several biological mechanisms to promote cross-pollination and prevent self-fertilization:

• Dichogamy: Maturation of stamens and pistils occurs at different times. Examples: Protandry (Sunflower, Mustard) — stamens mature first; Protogyny (Peepal, Mirabilis) — pistil matures first.
• Herkogamy: Structural barrier between stamens and stigma prevents contact, e.g., in Hibiscus and Gloriosa.
• Self-incompatibility: Pollen from the same plant is unable to fertilize its own stigma due to genetic mechanisms (seen in Brassica species).
• Heterostyly: Flowers have styles and stamens of different lengths, ensuring cross-pollination (as in Primula).
• Male sterility: Some plants produce functionally sterile pollen to encourage pollen transfer from other flowers.

Summary: These adaptations maintain genetic diversity and reduce inbreeding in bisexual species.