Laurel
A wreath of laurel on Kirk's head
Laurel wreath surrounding a star map of the Federation
Laurel was a plant native to the Mediterranean region of Earth. During the Golden Age of ancient Grecian and Roman Empires, laurel wreaths were given as prizes to respected and noble individuals. These were worn on the head like a crown.
Greek gods and their hybrid descendents had an immovable bioluminescent constructs on their heads which resembled "laurels". Following the demise of Apollo, Captain Kirk regretfully wondered if they should have gathered some laurel leaves for Apollo, rather than destroy him. (TOS: "Who Mourns for Adonais?")
Kirk and Spock were forced to wear laurel wreaths on their head by Parmen, during his attempt to force them to allow Doctor McCoy to remain on Platonius. (TOS: "Plato's Stepchildren")
The laurel wreath appears in the design for the Great Seal of the Federation.