A harmful lichen is

Options

A. Umbilicaria
B. Letharia
C. Usnea
D. Cladonia

Answer

### Step-by-Step Solution:

1. **Understanding Lichens**:
- Lichens are symbiotic associations between fungi and algae. The algae (which can be blue-green or green) perform photosynthesis to produce food, while the fungi provide structural support and absorb water and minerals.

2. **Identifying Types of Lichens**:
- Lichens can be classified into different genera. Some examples mentioned in the transcript include Amblycaria, Litheria, Asnea, and Cladonia.

3. **Analyzing the Options**:
- The question asks for a harmful lichen. The transcript discusses several lichens:
- **Amblycaria**: Not harmful, used in folk medicine.
- **Litheria (specifically Litheria vulpina)**: Produces a toxic compound called vulpinic acid, which is harmful to mammals, including wolves and foxes.
- **Asnea**: Known for its medicinal properties and antibiotic effects, thus not harmful.
- **Cladonia**: Also has antibiotic properties and is used medicinally, hence not harmful.

4. **Conclusion**:
- Based on the information provided, the harmful lichen identified is **Litheria vulpina** due to its production of the toxic vulpinic acid.

5. **Final Answer**:
- A harmful lichen is **Litheria vulpina**.