Explain dichogamy with example.

Dichogamy refers to a reproductive phenomenon in plants where the male and female reproductive organs of a flower mature at different times, thus reducing the chances of self-fertilization and promoting cross-pollination. This strategy enhances genetic diversity within a plant population, which can be beneficial for the survival and adaptation of the species.

There are two main types of dichogamy:

Protandry: In this type, the male reproductive organs (anthers) mature before the female reproductive organs (stigma). This temporal separation reduces the likelihood of a flower's own pollen reaching its stigma and promotes cross-pollination. A common example of protandry can be found in the sunflower family (Asteraceae). In a sunflower head, the outer ray florets often have mature anthers before the central disk florets have receptive stigmas, preventing self-fertilization and encouraging pollinators to transfer pollen between different flowers.

Protogyny: This type is the opposite of protandry. Here, the female reproductive organs (stigma) mature before the male reproductive organs (anthers). This again minimizes the chances of self-fertilization and encourages cross-pollination. A well-known example of protogyny can be seen in many species of holly (Ilex), where the stigma becomes receptive before the anthers release pollen.

Dichogamy is an evolutionary adaptation that enhances genetic diversity by promoting outcrossing (cross-pollination between different plants) and reducing the potential negative effects of inbreeding. It increases the chances of introducing new genetic variations into the population, which can be crucial for the species' ability to adapt to changing environmental conditions.