If comparing a river system to a tree, what tree part represents the tributary? flower branch bark leaf

The answer is 'Leaf'. River tributaries are the smallest parts of rivers, such as streams, that lead into a larger river. Headwater catchments contain tributaries, but tributaries may also occur all along the length of a river, and feed into the main stem of the river, depending on the land elevation. This is similar to a tree leaf. Leaves contain tiny veins, that join to form thicker veins, that then move into the branch and finally the main stem.

What have scientists learned about plant behavior by studying the dodder plant