Also just a fun note, I learned that willow flowers (plant 4) are reduced and therefore do not have sepals or petals, and are in clusters that truly don’t look much like flowers at all – called catkins! The name catkin comes from the Dutch word for kitten (katteken). Here’s a cute illustration that I found a few years ago – how fitting!
Nice job on your key! I found it simple, clear and easy to use. My only comment is that I’m not sure if I would have classified Plant 4 as a plant with “Flowers without petals”, but that didn’t impede the usefulness of the key.
I also love the comment and picture of the catkins, such a fun random plant fact!