We are given the statement: "All flowers are leaves" and "Some leaves are green".
From the first statement, we know that all flowers are leaves, but this does not mean that all leaves are flowers. Hence, Conclusion II ("All leaves are flowers") is incorrect.
For Conclusion I: "Some flowers are green", since "Some leaves are green" and all flowers are leaves, it is logical that some flowers could be green as well. Therefore, Conclusion I follows.
Answer: \(\boxed{A}\)