Which of the following conditions in flowering plants enhance self-pollination?

Analyzing the question

The question asks which condition promotes self-pollination, where pollen from a flower lands on the stigma of the same flower (or another flower on the same plant).

Explaining the concepts

• Cleistogamy: The flower never opens (it stays closed). Pollination and fertilization happen inside the closed bud, so pollen can only reach the stigma of the same flower. This guarantees self-pollination. Examples: some violets, groundnut (peanut), and some grasses.
• Heterostyly: Flowers on different plants have styles of different lengths (e.g., pin and thrum flowers in primrose). This arrangement makes it hard for a flower to pollinate itself and promotes cross-pollination.
• Protandry: The anthers mature and release pollen before the stigma of the same flower is ready. This prevents self-pollination and favors cross-pollination. Example: sunflower.
• Protogyny: The stigma matures before the anthers release pollen. This also favors cross-pollination. Example: some Nigerian plants like pawpaw varieties and avocado.

Solution

Going through the options one by one:

• A: Cleistogamy → self-pollination ✔
• B: Heterostyly → cross-pollination ✘
• C: Protandry → cross-pollination ✘
• D: Protogyny → cross-pollination ✘

Only cleistogamy ensures that pollen stays within the same flower, so it is the condition that enhances self-pollination.

Exam tip

Remember: "Cleisto = Closed", so the flower is closed and pollinates itself. Any condition involving timing differences (protandry and protogyny) or structural differences (heterostyly) between male and female parts is designed to promote cross-pollination.