Herb
May in flower and blood in fruit — the fairy tree of the English field.
These are associations the community holds, not settled fact — the more a reading is shared, the bolder it sits.
Hawthorn is the tree the English calendar is organised around. It flowers when the season turns, and the old name for the blossom is simply May. Bringing it indoors was widely held to be unlucky, a taboo strong enough that it was still being reported in the twentieth century, and it may have something to do with the smell — hawthorn blossom contains a compound also produced by decaying flesh, which people noticed long before anyone could name it.
Solitary thorns standing in the middle of Irish and British fields are still left uncut, and roads have genuinely been rerouted around them within living memory. The tree marks boundaries, holy wells and gathering places, and in Ireland is the fairy thorn above all others. Where hawthorn, oak and ash grow together, the old rule is that you are somewhere worth being careful.
Craft use is protection, threshold work and matters of the heart, the last complicated by hawthorn's genuine and well-documented pharmacological activity on the cardiovascular system — which is exactly why it is not a plant to experiment with.
Readings practitioners have offered, ordered by how many recognise them. Take what serves, leave the rest.
Carried forward
Irish and British field lore
A lone thorn in open ground is left standing, and cutting one is held to bring misfortune. Road schemes have been altered rather than fell one, which makes this among the few pieces of tree lore with a documented effect on civil engineering.
Carried forward
Nicholas Culpeper, The Complete Herbal (1653)
Culpeper states simply that "It is a tree of Mars", and recommends the seeds beaten to powder against the stone and the dropsy. The heart association he does not make; that is later, and in this rare case it turned out to be pointing at something real.
Credit what you carry. Much of this comes from living traditions, and some of it from traditions that are closed — held by particular peoples and not offered for general use. Where you know whose practice a reading came from, name them; where you don't, say that too.