To solve this problem, we need to analyze each statement regarding gymnosperms and related plants:$\newline \bullet$Option 1: Gymnosperms are both homosporous and heterosporous.$\newline$ - Gymnosperms are typically heterosporous, meaning they produce two types of spores: microspores and megaspores.$\newline$ - Therefore, this statement is incorrect.$\newline \bullet$Option 2: Salvinia, Ginkgo and Pinus all are gymnosperms.$\newline$ - Salvinia is actually a genus of aquatic ferns, which are pteridophytes, not gymnosperms.$\newline$ - Ginkgo and Pinus are gymnosperms.$\newline$ - Therefore, this statement is incorrect.$\newline \bullet$Option 3: Sequoia is one of the tallest trees.$\newline$ - Sequoia, particularly Sequoiadendron giganteum, is known for being one of the tallest trees in the world.$\newline$ - Therefore, this statement is correct.$\newline \bullet$Option 4: The leaves of gymnosperms are not well adapted to extremes of climate.$\newline$ - Gymnosperms, such as conifers, have leaves that are well adapted to extreme climates.$\newline$ - Their leaves are often needle-like or scale-like, which helps reduce water loss.$\newline$ - Therefore, this statement is incorrect.$\newline$Based on the analysis, the correct statement is Option 3: Sequoia is one of the tallest trees.