Named in Hortulus and Capitulare de villis
Rue
Ruta graveolens
What was written
Rue appears in the Hortulus as a counter to poison, a role it held in classical writing long before the monasteries inherited it and kept for centuries after. It is one of the plants the Capitulare de villis orders grown on every royal estate, which places it among the fixed furniture of an early medieval garden rather than a speciality.
What is now known
Rue is phototoxic. The furanocoumarins in its sap react with sunlight and cause severe blistering burns on skin that has touched it — a well-documented injury among gardeners today, not a historical curiosity. It has also long been used to induce abortion, at doses close to those that cause serious poisoning. Handle it with gloves and do not ingest it.
The plant itself
A blue-green evergreen subshrub with rounded, deeply divided leaves and a strong, bitter scent that carries several paces on a warm day.
Still growing
Since the plant was written into that garden list, botanists, herbaria and ordinary observers have recorded finding it 8,842 times.
Live count from GBIF, cached for a week.