In a bisexual flower, when the androecium (male whorl) and gynoecium (female whorl) mature at different times to prevent self-pollination, the phenomenon is known as what?

Introduction / Context:
Flowering plants have evolved various mechanisms to promote cross pollination and reduce self pollination, which increases genetic diversity. In bisexual flowers, both male and female reproductive parts are present in the same flower, so plants may adopt timing or spatial strategies to reduce self fertilisation. One important timing mechanism involves the male and female parts maturing at different times. This question asks you to identify the term used for that timing based mechanism.

Given Data / Assumptions:

• The flower in question is bisexual, containing both androecium and gynoecium.
• The androecium and gynoecium mature at different times.
• Options include dichogamy, herkogamy, heterogamy, monogamy, and none of these.
• We assume standard botanical terminology used in pollination biology.

Concept / Approach:
Dichogamy is the term used when the male and female parts of a bisexual flower mature at different times. It can be of two types: protandry, where anthers mature first, and protogyny, where stigma matures first. Herkogamy refers to structural or spatial separation between anthers and stigma within the flower to prevent self pollination. Heterogamy more generally refers to the presence of different kinds of individuals or gametes, and monogamy is a term used in animal behaviour and human society, not in floral biology. Therefore, the correct answer to a timing based difference in maturity is dichogamy.

Step-by-Step Solution:
Step 1: Focus on the key phrase: androecium and gynoecium mature at different times in a bisexual flower. Step 2: Recall that dichogamy is defined as the difference in time of maturity of male and female sex organs in the same flower. Step 3: Understand that this timing difference reduces chances of self pollination, because pollen is unlikely to land on a receptive stigma of the same flower at the same time. Step 4: Recognise that herkogamy describes spatial or structural separation, not timing. Step 5: Note that heterogamy and monogamy are not standard terms used for this specific floral phenomenon. Step 6: Therefore, select dichogamy as the correct answer.

Verification / Alternative check:
Botany textbooks on pollination and fertilisation in angiosperms describe several mechanisms promoting cross pollination. They explicitly list dichogamy as a temporal mechanism, explaining protandry and protogyny with examples such as sunflower or certain plants where stamens ripen earlier. Herkogamy is described separately, often with examples where the physical positions of anther and stigma reduce self pollination. This clear distinction supports dichogamy as the correct term for differing maturity times in a bisexual flower.

Why Other Options Are Wrong:
Herkogamy: Refers to spatial separation of anther and stigma, not differences in time of maturity. Heterogamy: A broader term meaning presence of different types of gametes or individuals, not specifically timing differences in a single flower. Monogamy: A social or reproductive term mostly used for animals and humans, not for timing of flower whorls. None of these: Incorrect because dichogamy precisely describes the phenomenon in the question.

Common Pitfalls:
Students often confuse dichogamy with herkogamy because both reduce self pollination. Mixing up temporal and spatial mechanisms is a frequent error. Memorising simple associations helps: dichogamy relates to time (different maturation times), while herkogamy relates to space (different positions). When the question mentions maturity at different times, dichogamy is the key word to remember.

Final Answer:
The correct answer is Dichogamy.