Although rue grows wild here in Spain, I've not used it in the kitchen and its main use locally seems to be medicinal, including for illegal abortions.
Mediterranean or Western Asia.
Rue is found wild across the Mediterranean region and parts of Western Asia.
Fresh leaves. If not available, dried leaves are a poor substitute. The fruits of rue are rarely used in the kitchen.
Rutaceae (citrus family).
The fragrance of rue is strong, characteristically sweetly aromatic and cannot be compared with that of any other spice. The taste is rather bitter and even more so when dried. Rue fruits (berries) have a similar taste but are stronger and somewhat hot.
Most Western European languages have similar names for rue, e.g. French rue, Dutch ruit and German raute which are all derived from Latin ruta, itself was loaned from Greek rhyte. The ultimate origin of the word is not known. Several names of rue have unintentional homonyms, e.g. English "rue" or "remorse", French rue "street" and German raute "rhomboid".
In the New Testament rue is mentioned as peganon, a name still used in Modern Greek as apiganos. There have been attempts to link that name with Greek pegos "strong" and thence to the Indo-European root pek "strengthen", but the connection is unclear. Related names include the French péganium, Hebrew pegam and Arabic fayjan.
The Turkish name of rue, sedefotu, appears to mean "mother-of-pearl herb" (sedef "mother of pearl" and otu "aromatic herb"). This may be motivated by the bluish hue of the rue leaves. The Turkish name was loaned to Bulgarian as sedefche and other related words can be found from Western Asia (Kurdish sudab), Central Asia (Farsi sadab) and South India (Telugu sadapa).
Rue belongs to the group of culinary herbs whose use in the kitchen is limited by their inherent bitterness. Rue was a very common spice in Ancient Rome, often being used for country-style food such as moretum, a spicy paste of fresh garlic, hard cheese and herbs (coriander, celery and rue). Its name was often used metonymically for "bitterness" (especially in poetry) and the level of use has declined since Roman times, with almost universal rejection today. This failure is despite the plant's inclusion on the list of herbs grown across Europe during the Middle Ages in accordance with Charlemagne's Capitulare de Villis.
Apart from occasional use in Italy, the popularity of rue is greatest in Ethiopia, where fresh rue leaves are used as a coffee flavorant and rue is also used as a component of the national spice mix berbere. Ethiopian cuisine is unique in using not only rue leaves, but also the dried fruits (rue berries) which have a more intensive, slightly pungent flavour preserved on drying.
Cooking with rue today is considered old-fashioned by the young, although one reason for this is that a palate for bitter tastes generally develops as people become older. Rue is definitely worth trying and meat, eggs and cheese can all profit from this almost unknown spice, provided care is taken not to overdose. The bitter taste is reduced by acids, so rue leaf may be used to flavour pickled vegetables or make a salad vinaigrette more interesting. Because of its general affinity to acidic food, rue also goes well with spicy Italian tomato sauces containing olives and capers (together with marjoram, basil and lovage).
To achieve rue flavour without bitterness the fresh leaves may be soaked in a slightly boiling sauce for a short time and then discarded. This works because rue leaves excrete their essential oil much more quickly than the bitter rutin (as with tea leaves).
Like many other bitter spices, rue is popular for flavouring liqueurs. Besides stimulating the appetite, bitter liqueurs have some tonic and bile-stimulating properties, which are advantageous after a rich feast. One of the most common liqueurs containing rue is grappa con ruta, an Italian brandy flavoured with a small branch of rue per bottle. The related plant r. chalepensis (fringed rue) is usually preferred for this purpose.
Rue should not be confused with southernwood, a bitter herb with a stronger, more lemon-like fragrance. Neither plant is of great culinary importance and both are considered potentially poisonous (although their toxicity may be neglected in amounts used for cooking). Extreme overdoses of pure essential oil of rue have been reported to cause abortion and the plant was once called herbe à la belle fille "herb of fair maidens" in France in reference to this.