The blackthorn, Prunus spinosa, is a dense, viciously spined shrub of European hedgerows, its bare black twigs whitening with blossom very early in spring before the leaves, and bearing in autumn the sloes, small bitter blue-black plums used to flavour gin. Set against the white-blossomed hawthorn of May, the blackthorn was read as its dark twin: a tree of winter, hardship and the waning year, associated in Celtic folk tradition with the Cailleach, the old woman of winter, who was said to strike the ground with a blackthorn staff.
The Tyrolean Iceman Otzi, whose 5,300-year-old body was found preserved in an Alpine glacier in 1991, was carrying a sloe among his possessions and had eaten blackthorn fruit not long before he died, physical evidence that people were gathering the tart little fruit as food in the Alps in the Copper Age, millennia before any of the tree's later folklore was written down. English country tradition also names a specific cold snap after the tree: a blackthorn winter is the spell of cold, often bitter weather that reliably arrives just as the blackthorn comes into flower each March or April, a weather pattern noted in print at least since the 1820s and still spoken of by country gardeners today.