Which of the following characteristics is used to distinguish individual species of trees?

The characteristic that is primarily used to distinguish individual species of trees is the leaves. Leaf morphology—such as shape, size, arrangement, and type (broadleaf vs. needle-like)—provides critical identification information for different tree species. Tree leaves can vary significantly among species, allowing for easy differentiation based on their distinct physical traits.

Other characteristics like climate, soil type, and location, while relevant to understanding a tree's growth conditions and ecological niche, do not serve as definitive markers for identifying individual species. For example, multiple species may thrive in the same climate or soil type, and location alone does not provide sufficient detail for classification. Thus, examining the leaves of a tree provides the most direct and practical means of identifying the species.