Farfetch'd, Galarian Farfetch'd, and Sirfetch'd hold leeks*
Regigigas has moss on it*
The Flabébé line attaches itself to flowers
Pancham and Pangoro use leaves in battle and hold them in their mouths*
Skrelp and Dragalge are based on kelp
Comfey has a flower lei
Oranguru has a leaf fan*
Komala has a log*
Celesteela is partially based off bamboo
Kartana is origami, which comes from paper, which comes from trees*
Hope I helped!
*= debatable. They interact with plants in some way, but are not exactly based on plants.