How do flowering plants prevent self-fertilisation?

Flowering plants prevent self-fertilisation through mechanisms such as self-incompatibility, dichogamy, and herkogamy.

Flowering plants have evolved various strategies to prevent self-fertilisation, also known as selfing, and promote cross-fertilisation. This is crucial as it increases genetic diversity, which is beneficial for the survival and adaptation of species. One of the primary mechanisms is self-incompatibility. This is a genetic mechanism that recognises and rejects the plant's own pollen, thus preventing self-fertilisation. The plant's stigma, the female reproductive organ, can identify the pollen from the same plant or closely related individuals and inhibit its growth.

Another mechanism is dichogamy, where the timing of male and female reproductive maturity differs. In protandry, the male organs (anthers) mature before the female organs (stigmas), while in protogyny, the female organs mature first. This temporal separation reduces the chances of a flower's pollen fertilising its own ovules.

Herkogamy is a physical barrier to self-fertilisation. It involves the spatial separation of the male and female reproductive organs within a flower. For example, the anthers may be positioned far from the stigma, or the stigma may be enclosed within a structure that prevents it from coming into contact with its own pollen.

Flowering plants may also employ a strategy called heterostyly, where different individuals of the same species have different lengths of styles (the part of the flower connecting the stigma to the ovary) and stamens (the male reproductive organ). This ensures that pollen from one flower is unlikely to land on the stigma of a flower with the same style length, thus promoting cross-fertilisation.

In addition to these, some plants have evolved to produce unisexual flowers, which contain either male or female reproductive organs but not both. This is another effective way to prevent self-fertilisation.

In summary, flowering plants have developed a range of ingenious strategies to prevent self-fertilisation and promote cross-fertilisation, thereby enhancing their genetic diversity and adaptability.