The rowan, Sorbus aucuparia, also called mountain ash though it is unrelated to the true ashes, is a hardy tree of high and northern country bearing dense clusters of orange-red berries. Across Scotland, Scandinavia and the wider northern world it is the apotropaic tree above all others: planted by the door, made into crosses bound with red thread, and hung over byre and cradle to turn away witchcraft and the evil eye. The Scots rhyme rowan tree and red thread gars the witches tyne their speed records the belief exactly. Part of the reason offered is a natural mark, the base of each rowan berry carries a tiny five-pointed star, a pentagram, read as a protective sign.
Rowan berries are a genuine food as well as a charm: raw, they contain parasorbic acid, which causes stomach upset, but cooking breaks the compound down, and rowan jelly, a tart preserve traditionally served with game meat, has long been made across Scotland and Scandinavia from the same berries hung over doorways for protection, a case of the same fruit serving a practical culinary purpose and a magical apotropaic one side by side. Rowan is also a genuine pioneer species: it tolerates poor, thin soil and grows at higher altitudes than almost any other tree native to Britain, often the last tree standing on an exposed mountainside, an ecological toughness that sits well beside its old reputation as the tree most trusted to stand guard against harm.