Simply put in ancient cultivation and even in modern fields, drought and sun exposure dry out the leaf and the serrations wither and disappear. Also when the leaves are picked, the edges curl in on themselves. The above coin is a Hemidrachm from Thessaly, Lamia (350-300 BC). One can see the "ivy leaf" which makes no sense whatsoever. It is really a harvested opium poppy leaf on the crown of Dionysus on the obverse and above the beaded rim pot on the reverse. Cut the poppy head off and put it in the amphora is the message. Wine and poppies were a very common theme in Ancient Greece.
Opium leaves on the coins of Herod the Great, Fontanille Coins
First Photo Numismatik-Naumann, V coins