Name an aquatic angiosperm where the roots are absent.

Explanation

### Step-by-Step Solution:

1. **Identify the Type of Plant**: The question asks for an aquatic angiosperm, which is a flowering plant that grows in water.

2. **Understand the Characteristics**: The specific characteristic mentioned is that the plant must have no roots. This means we are looking for a unique adaptation among aquatic plants.

3. **Recall Aquatic Angiosperms**: Think of common aquatic angiosperms. Some examples include water lilies, duckweeds, and others. However, we need to focus on those that lack roots.

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