While working on his painting Leda and the Swan, Leonardo created several sketches of plants, such as A star-of-Bethlehem and other plants (c.1506-12), in order to better represent them within his painting.  Sketches These sketches show a high level of detail that later carries into his art and pays close attention to the form and structure of plants and how that can change for each one. These sketches have been collected and held on to by the Windsor Castle Royal Collection since the 17th Century.

Image from Wikimedia Commons, commons.wikimedia.org/wiki/File:Leonardo_da_vinci,_Star_of_Bethlehem_and_other_plants.jpg. This image is under public domain and free use.