This thread reminds me of two incidents in military history; At the battle of Minden on 1 August 1759, British soldiers reportedly plucked roses and wore them in their hats as they went into combat. The event was commemorated by the regiments (including the old KOSBs) on the anniversary with officers & ORs wearing a rose in their hats.

At the battle of Fredericksburg in the American Civil
War, members of the Irish Brigade wore springs of
Boxwood in their hats as they made the disasterous
charge up Mayre's Heights.

Not really a connection to Highland clans, but certainly similar to the OP.

T.