…and the Gregorian calendar!
It used to be expected that H. niger would bloom near the date we now think of as 6 January. Under the old Julian calendar, this was Christmas Day.
So, when the new Gregorian calendar came around, and Christmas Day became 25 December, the flower was not yet in bloom. This was considered such a terrible omen that England did not fully adopt the new calendar for around another 180 years – until 1751.