Which of the following algae reproduce asexually by non-motile spores only?

Options

A. Dictyota
B. Ectocarpus
C. Ulothrix
D. Polysiphonia

Answer

To solve the question, "Which of the following algae reproduce asexually by non-motile spores only?" we will analyze the options provided and determine which one fits the criteria of reproducing asexually with non-motile spores.

### Step-by-Step Solution:

1. **Identify the Options**: The options given are:
- A) Dictyota
- B) Ectocarpus
- C) Ulothrix
- D) Polysiphonia

2. **Classify the Algae**:
- **Dictyota**: This is a brown algae (Phaeophyceae) known to reproduce asexually via motile spores (flagellated).
- **Ectocarpus**: Another brown algae that also reproduces asexually using motile spores (flagellated).
- **Ulothrix**: This is a green algae (Chlorophyceae) that reproduces asexually through quadriflagellated (four flagella) spores, which are motile.
- **Polysiphonia**: This is a red algae (Rhodophyceae) that reproduces asexually using non-motile spores.

3. **Determine the Mode of Reproduction**:
- Red algae, such as Polysiphonia, lack motile cells in their life cycle. They reproduce asexually using non-motile spores.
- Brown algae (Dictyota and Ectocarpus) and green algae (Ulothrix) have motile spores.

4. **Conclusion**: Based on the classification and reproduction methods:
- The only algae that reproduce asexually by non-motile spores only is **Polysiphonia**.

### Final Answer:
The correct answer is **D) Polysiphonia**.