Liquidamber leaves are one of my favorites for my leaf monoprints. The trees are deciduous, and the leaves turn various shades of yellow and red before they fall.
Look for deep red leaves that are fresh, and not brown or dried out. The deep red leaves work the best for leaf monoprints.
The liquidamber leaves have several different looks, depending on which side of the leaf is pressed against the paper. Here are some liquidamber monoprints on India and Fabriano watercolor papers.