The mismatched pair among the following is :

Options

A. Monadephous - Hibiscus
B. Diadelphous - Cucurbita
C. Polyadelphous - Citrus
D. Variation in the length of stamen filaments - Salvia

Answer

To solve the question regarding the mismatched pair among the given options, we need to analyze each pair carefully.

### Step-by-Step Solution:

1. **Understanding the Terms**:
- **Monodelphous**: Refers to stamens that are united into a single group or bundle.
- **Didelphous**: Refers to stamens that are divided into two groups.
- **Polydelphous**: Refers to stamens that are divided into several groups.
- **Synandrous**: Refers to stamens that are fused along their entire length.

2. **Analyzing Each Option**:
- **Monodelphous, Hibiscus**: In Hibiscus, the stamens are indeed monodelphous as they form a single bundle while the anthers remain free. This is a correct match.
- **Didelphous, Cucurbita**: In Cucurbita, the stamens are not didelphous; they are actually synandrous, meaning they are fused along their entire length. This is a mismatched pair.
- **Polydelphous, Citrus**: In Citrus, the stamens are indeed polydelphous, as they form several small bundles. This is a correct match.
- **Variation in Length of Stem and Filaments**: This characteristic is typically seen in Salvia, not in the other options provided. However, it is not a mismatched pair as it refers to a different aspect.

3. **Identifying the Mismatched Pair**:
- The only mismatched pair from the options provided is **Didelphous, Cucurbita**. Cucurbita does not exhibit didelphous stamens; instead, they are synandrous.

### Final Answer:
The mismatched pair among the following is **Didelphous, Cucurbita**.