Because diadelphous condition is found in the family of Fabaceae and petunia is an example of the family solanaceae.

Diadelphous Flower

The term "diadelphous" refers to a specific type of flower structure found in certain flowering plants. In diadelphous flowers, the stamens are fused together into two separate bundles or groups. These bundles are usually unequal in length, with one bundle containing nine stamens and the other containing only one stamen. This unique arrangement is characteristic of the family Fabaceae, which includes many well-known plants such as peas, beans, and lentils.

Options:

a) Pea
b) Petunia
c) Sesbania
d) Groundnut

Correct Answer: Option B (Petunia)

Explanation:

- Pea (Pisum sativum): Pea flowers are diadelphous, meaning their stamens are fused into two groups. One group consists of nine stamens fused together, while the other group contains only one separate stamen. Therefore, the diadelphous flower structure is present in peas.

- Petunia: Petunias, on the other hand, do not exhibit a diadelphous flower structure. Instead, their stamens are not fused together and are usually arranged in a whorl around the pistil. Each stamen is separate and not grouped into bundles. Therefore, petunias do not have diadelphous flowers.

- Sesbania: Sesbania flowers are also diadelphous, similar to peas. The stamens are fused into two separate groups, with one group containing nine stamens and the other containing a single stamen. Therefore, the diadelphous flower structure is present in Sesbania.

- Groundnut (Arachis hypogaea): Groundnut flowers also exhibit a diadelphous flower structure. The stamens are fused into two groups, with one group consisting of nine stamens fused together, and the other group containing a single stamen. Therefore, the diadelphous flower structure is present in groundnuts.

In conclusion, the correct answer is option B (Petunia), as it is the only plant among the given options that does not possess a diadelphous flower structure. The other options, such as pea, sesbania, and groundnut, all have diadelphous flowers with fused stamens arranged in two distinct groups.