The Glastonbury thorn is a form of common hawthorn, Crataegus monogyna 'Biflora', found in and around Glastonbury, Somerset, England. Unlike ordinary hawthorn trees, it flowers twice a year, 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.

Crataegus monogyna, known as common hawthorn, one-seed hawthorn, or single-seeded hawthorn, is a species of flowering plant in the rose family Rosaceae. It is native to Europe, northwestern Africa, and Western Asia, but has been introduced in many other parts of the world.