What is "glastonbury thorn"

Glastonbury thorn \Glas"ton*bur*y thorn`\ (Bot.) A variety of the common hawthorn.
--Loudon.

The Glastonbury thorn is a form of common hawthorn, Crataegus monogyna 'Biflora' (sometimes incorrectly called Crataegus oxyacantha var. praecox), found in and around Glastonbury, Somerset, England. Unlike ordinary hawthorn trees, it flowers twice a year (hence the name "biflora"), the first time in winter and the second time in spring. The trees in the Glastonbury area have been propagated by grafting since ancient times. The tree is also widely called the holy thorn, though this term strictly speaking refers to the original (legendary) tree.

It is associated with legends about Joseph of Arimathea and the arrival of Christianity in Britain, and has appeared in written texts since the medieval period. A flowering sprig is sent to the British Monarch every Christmas. The original tree has been propagated several times, with one tree growing at Glastonbury Abbey and another in the churchyard of the Church of St John. The "original" Glastonbury thorn was cut down and burned as a relic of superstition during the English Civil War, and one planted on Wearyall Hill in 1951 to replace it had its branches cut off in 2010.