Oak Apple Day
Public holiday in England on 29 May to celebrate the Restoration of the English monarchy; it was formally abolished in 1859. An oak apple is caused by the larvae of a gall wasp, they are so called because the gall slightly resembles an apple.
Origin
Followers of the monarchy celebrated Charles II's birthday and his escape from the Roundheads on 29 May. It was called 'Oak Apple Day' in remembrance of the time when Charles hid in an oak tree following the Battle of Worcester on 3 September 1651 and evaded being captured by marauding soldiers [please indicate the source]. Charles remembered the tree and declared the holiday in its honor, the parliament stating:
“Parliament had ordered the 29th of May, the King's birthday, to be for ever kept as a day of thanksgiving for our redemption from tyranny and the King's return to his Government, he entering London that day.” [exact source??]
Samuel Pepys (1660)
Today
Today, it is practice for monarchists to decorate the house with oak branches or wear an oak branchlet on May 29 [please indicate the source]. In All Saints Church in Northampton, for example, a wreath of oak-apples is laid at Charles II's statue [please indicate the source]. Its true origin is largely forgotten.
Sources
Rose, Jacqueline. Godly Kingship in Restoration England. The Politics of the Royal Oupremacy, 1660 - 1688. Cambridge: Cambridge University Press, 2011.