The design problem
The smallest German euro coins needed a national symbol that could survive at very small size. Rolf Lederbogen's answer was the oak twig, used on the 1, 2, and 5 cent pieces.
The oak already had a long life in German coinage. It appeared as leaves, wreaths, and civic symbolism across earlier currencies, including the Deutsche Mark. Lederbogen did not make it monumental. He made it botanical and compact: a twig, readable on copper-colored coins where elaborate detail would fail.