Select the correct statement. from the following .

Options

A. Gymnosperm are both homosporous and hetersporous.
B. Marsilea, Ginkgo and Pinus all are gymnosperms
C. The leaves of gymnosperms are not well adapted to extremes of climate.
D. The giant redwood tree Sequoia is one of the tallest tree species.

Answer

To solve the question, we need to analyze each statement provided in the options and determine which one is correct.

### Step-by-Step Solution:

1. **Evaluate Option A**: "Gymnosperms are both homosporous and heterosporous."
- **Analysis**: Gymnosperms are primarily heterosporous, meaning they produce two types of spores: microspores (male) and megaspores (female). Therefore, this statement is incorrect.

2. **Evaluate Option B**: "Marcelia, Ginkgo, and Pinus all are Gymnosperms."
- **Analysis**: Ginkgo and Pinus are indeed gymnosperms, but Marcelia is a genus of aquatic ferns, not a gymnosperm. Thus, this statement is also incorrect.

3. **Evaluate Option C**: "The leaves of Gymnosperms are not well developed to the extremities of climate."
- **Analysis**: This statement is misleading. Gymnosperms have leaves that are well adapted to extreme climates, including cold and dry conditions. Therefore, this statement is incorrect.

4. **Evaluate Option D**: "The giant redwood tree sequoia is the tallest tree species."
- **Analysis**: This statement is correct. The giant redwood (Sequoiadendron giganteum) is indeed known as the tallest tree species in the world.

### Conclusion:
The correct statement is **Option D**: "The giant redwood tree sequoia is the tallest tree species."