Which one of the following is the unique feature of angiosperms?

Options

A. haploid endosperm
B. Circinate vernation
C. Coralloid roots
D. Double fertilization

Answer

To determine the unique feature of angiosperms, we can analyze the options provided in the question:

### Step-by-Step Solution:

1. **Understanding Angiosperms**: Angiosperms, also known as flowering plants, are characterized by the presence of flowers and seeds enclosed within a fruit. They are the most diverse group of land plants.

2. **Analyzing the Options**:
- **Option 1: Haploid Endosperm**: In angiosperms, the endosperm is typically triploid (3N) due to double fertilization. In gymnosperms, the endosperm is haploid (1N). Thus, this is not a unique feature of angiosperms.
- **Option 2: Circinate Venation**: This refers to the way leaves develop in certain plants, particularly ferns. It is not a characteristic of angiosperms.
- **Option 3: Coralloid Root**: This type of root is found in some gymnosperms, specifically cycads. Therefore, it is not unique to angiosperms.
- **Option 4: Double Fertilization**: This is a defining characteristic of angiosperms. In this process, one sperm fertilizes the egg to form a diploid zygote (2N), while another sperm fuses with two polar nuclei to form the triploid endosperm (3N).

3. **Conclusion**: The unique feature of angiosperms is **double fertilization**.

### Final Answer:
The unique feature of angiosperms is **double fertilization**.