Assertion: Arboretum is the ex-situ conservation strategy of plants.
Reason: It is a special kind of garden with main collection of herbs and shrubs.

Answer

### Step-by-Step Solution:

1. **Understanding the Assertion:**
- The assertion states that "Arboretum is the ex-situ conservation strategy of plants."
- Ex-situ conservation refers to the conservation of species outside their natural habitats. Arboretums are designed to cultivate and conserve tree species, making this assertion true.

2. **Understanding the Reason:**
- The reason states that "It is a special kind of garden with the main collection of herbs and shrubs."
- An arboretum is specifically a botanical garden focused on trees, not herbs and shrubs. Therefore, this statement is false.

3. **Analyzing the Relationship:**
- Since the assertion is true and the reason is false, we conclude that while the assertion about arboretum being an ex-situ conservation strategy is correct, the reason provided does not accurately describe what an arboretum is.

4. **Final Conclusion:**
- The assertion is true, and the reason is false. Thus, the correct response to the question is that the assertion stands alone as true, while the reason does not support it.