The study looked at different traits of plant leaves in a wetland in Beijing. They found that certain leaf traits were related to each other, and could be grouped into two main categories and one separate trait. The first group included traits like leaf weight, area, and thickness, while the second group included specific leaf area and leaf dry matter content. Leaf nitrogen content was a separate trait. By using a method called hierarchical clustering, the researchers were able to group the plant species into four functional groups based on these traits. The specific leaf area and leaf dry matter content were important for classifying the plants into these groups.