Ruta chalepensis (PROTA)
|Geographic coverage Africa|
|Geographic coverage World|
|Spice / condiment|
- Protologue: Mant. pl. 1: 69 (1767).
- Family: Rutaceae
- Chromosome number: 2n = 36, 40
- Ruta bracteosa DC. (1824).
- Fringed rue (En).
- Rue de Chalep (Fr).
Origin and geographic distribution
Ruta chalepensis is indigenous to the Mediterranean region and the Canary Islands. It is cultivated in the tropics as a potherb or medicinal plant and has widely become naturalized. In tropical Africa it has been introduced in several countries, including the Cape Verde Islands, Sudan, Ethiopia, Somalia and southern Africa (including South Africa), where it is mostly cultivated in herbal gardens. It has also been naturalized in peninsular Arabia, India, Malaysia, Vietnam and Java. It has furthermore been naturalized in the United States, Mexico, Cuba and Chile.
In Africa, the morphologically and chemically related Ruta graveolens L. seems only to be present in South Africa.
Ruta chalepensis is cultivated in several countries in tropical Africa where it is used for cooking and medicinal purposes. The medicinal and culinary properties are attributed to the presence of essential oils which are contained in all parts of the plant. The tops of the fresh shoots are the most active and should be gathered before the plant flowers.
In northern Sudan, a fruit poultice is applied to swellings. In Ethiopia Ruta chalepensis is an important medicinal plant. An aqueous-alcoholic extract of the leaves is drunk as an anti-implantation and uterotonic medicine. A decoction of the pulverized fruits in milk is taken to treat diarrhoea. A root decoction in an alcoholic drink, with hot peppers, is taken to treat influenza. Plant sap is taken to treat stomach-ache. A leaf decoction with tea is taken to treat headache, fever and common cold. In southern Africa, the oil obtained from the aerial parts is applied externally as a rub to treat stomach-ache, colic, hysteria, epilepsy and is taken orally as an anthelmintic. Among the Tswana of southern Africa, a decoction of the whole plant in high doses is taken to ease childbirth. In South Africa, a leaf decoction of Ruta chalepensis or Ruta graveolens is taken for the treatment of typhoid and scarlet fever, whereas the leaf juice is given to children suffering from convulsions, fits, jaundice and diarrhoea. The crushed leaves are externally applied to treat toothache and earache. A maceration of the leaves is taken to treat cardiac and respiratory diseases, rheumatism, gout and hypertension. Leaves are taken in tea or chewed to treat stomach-ache and headache.
Ruta chalepensis and Ruta graveolens have traditionally been used for centuries as a condiment of food and alcoholic beverages in the Mediterranean region, but their use has much declined because of its bitterness. The fragrance of the leaves is strong, characteristically aromatic and sweet. The fruits taste similar, but stronger and somewhat hot. In Ethiopia fresh leaves of Ruta chalepensis are used as a flavouring of a beverage called ‘kuti’, which is an infusion of coffee leaves; the leaves are also a component of the spicy Capsicum sauce ‘berbere’. Washed leaves are added to sour milk to make a local cheese.
The plants can be planted to deter dogs and cats, as they hate the smell. The dried and crushed leaves are also an effective insect repellent.
Both the herb and its essential oils have been widely used in the past in Europe as an anthelmintic, stomachic, antispasmodic, anti-epileptic, rubefacient, emmenagogue and abortifacient. Excessive use of the herb is dangerous. Its toxic effects are clearly dose-dependent. It is potentially toxic and carcinogenic when consumed orally, and can produce dermatitis when touched. Used internally, the leaves and oil can cause haemorrhages, miscarriage and abortion, and have been used as such since ancient times. It may further cause vomiting, gastroenteritis, swelling of the tongue, coldness of the extremities, and even death. For some people, ingestion causes increased photosensitivity and can lead to severe sunburn.
The oil is used as a flavouring agent and in perfumes and soap scents. Oils, which are rich in methyl nonyl ketone are used for the preparation of methyl-n-nonyl acetylaldehyde, widely applied as a synthetic perfume.
The plant is also widely grown as ornamentals in hedges or as a container plant.
Production and international trade
Commercial production of essential oil from Ruta chalepensis and Ruta graveolens is centred in the Mediterranean region. In Ethiopia either dried fruits, or fresh or dried twigs with leaves, flowers and fruits are found commonly in the local markets.
The compounds isolated from Ruta chalepensis and Ruta graveolens are essentially the same, although quantitative differences are observed. However, these differences are of the same magnitude as those observed within the same species collected from different sources. Qualitative and quantitative differences are also found for the different parts of the plants. Both species are characterized by the presence of alkaloids (acridone-, quinolone-, furoquinolone-type alkaloids, and quaternary furoquinolines), (furano-)coumarins and essential oils. The essential oils from aerial parts of Ruta chalepensis plants harvested at different stages of growth in northern India contained 19 components, representing 85.4–93.3% of the oil. The major components were 2-undecanone (41.3–67.8%), 2-nonanone (5.2–33.6%), 2-nonyl-acetate (2.8–15.3%) and 2-dodecanone (<0.1–11.6%).
Major compounds isolated from the roots of Ruta chalepensis are the furoquinolin alkaloids kokusaginin, skimmianin and graveolin, the acridone alkaloids 1-hydroxy-N-methylacridone and chaloridon, and the furanocoumarin chalepensin. From the dried aerial parts, major compounds isolated include the furoquinolin alkaloids kokusaginin, skimmianin, graveolin, γ-fagarin and dictamnin, the acridone alkaloid arborinin, and the (furano-)coumarins bergapten (or 5-methoxypsoralen) and chalepensin.
Bergapten and chalepensin belong to the family of the linear furanocoumarins, which are known to have phototoxic activity. Dermatosis may arise after plant material containing these compounds comes into direct contact with the skin, if this is immediately followed by exposure to UV-A light, e.g. from the sun.
Ethanol extracts of air-dried flowering material have been studied in various models. Oral administration at a dose of 500 mg/kg significantly reduced carrageenan-induced oedema in rats. Similar results were reported using the cotton-pellet granuloma test model. Additionally, intraperitoneal administration at 100 mg/kg significantly reduced subcutaneously induced (yeast suspension) fever in mice. However, no analgesic activity was observed in the hot-plate test with mice. Of the isolated compounds, chalepensin at an intraperitoneal dose of 10 mg/kg significantly prolonged hexobarbital-induced sleeping time in mice. A hexane extract of the aerial parts showed strong molluscicidal activity against the schistosomiasis-transmitting snail Bulinus truncatus with an LC90 value of 2.23 mg/l. Ethanolic extracts furthermore showed in vitro activity against the bacteria Staphylococcus aureus and Pseudomonas vulgaris (disk diffusion assay).
Information on the antifertility effect of Ruta chalepensis presents a mixed picture. Whereas oral consumption of the essential oil induces abortion in guinea-pigs and humans, this probably can be attributed to a general toxic effect. The essential oil has no effect on the isolated uterus in (non-)pregnant cats or the isolated oviduct in (non-)pregnant women. An ethanol extract of the plant, however, shows a significant anti-implantation effect, an increased absorption rate and an overall reduced pregnancy ratio in albino rats. Petroleum ether and methanol extracts are reported to have similar results, whereas benzene and chloroform extracts merely have a toxicological effect. The antifertility effect is attributed to the furanocoumarin chalepensin, which has a very narrow therapeutical range.
Responsible for the bitter taste is rutin (7–8% in the dried leaves), a quercetin glycoside containing the disaccharide rutinose as sugar component. It is known for its capillary protection properties. Extracts of Ruta chalepensis have also been shown to possess anti-inflammatory properties.
Erect, densely branched subshrub 0.5–1(–1.5) m high. Leaves spirally arranged, 2–3-pinnatisect, obovate to oblong-obovate in outline, 4–15 cm × 2–9 cm, ultimate segments obovate-lanceolate, about 5–30 mm × 1.5–6 mm, conspicuously glaucous, crenate, translucent glandular punctate, strong smelling, lower leaves more or less petiolate, up to 12.5 cm long, 2(–3)-pinnate; stipules absent. Inflorescence a bracteate cyme, terminal or in the upper leaf axils, often combined into a corymb, bracts cordate-ovate, wider than the subtended branch. Flowers bisexual, 4(–5)-merous, protrandrous, central flowers 5-merous; pedicel 0.5–2 cm long; sepals deltate-ovate, 3–4 mm × 2–3 mm, glabrous; petals free, oblong, 4–8 mm long, fringed with cilia not as long as the width of the petal, greenish-yellow outside, yellow inside; anthers twice as many as the petals; ovary superior, almost round, 4–5-lobed, 3–5-celled. Fruit a 4-lobed capsule, 5–7 mm × 5–8 mm, segments acuminate, apically opening, 5–10-seeded. Seeds three-edged, kidney-shaped, dark brown or brownish-black. Seedling with epigeal germination.
Other botanical information
Ruta comprises about 8 species. The botanical identity of Ruta grown in tropical Africa is not always clear. The presence of the related Ruta graveolens in tropical Africa is based on misidentifications, certainly so in Ethiopia. The chemical composition of both species is almost identical. Ruta graveolens is a polyploid. The medicinal and culinary uses in South Africa are similar to those of Ruta chalepensis.
Ruta chalepensis grows well in well-drained sandy or rocky limestone soils and prefers an open sunny position. In Ethiopia it is cultivated at 1500–2000 m altitude.
Ruta chalepensis is mainly propagated by seed, but can also be reproduced by layering, division of roots and from cuttings. Taking cuttings is advantageous at lower elevations in the tropics where it is reported to flower rarely. Seed germinate (14–)45–60 days after sowing, and flowering starts 90–150 days later. Ruta chalepensis responds well to pruning and can be shaped into a rounded mass. In spring the plant can be pruned back to the old wood to encourage bushiness.
People dealing with harvesting should wear protecting gloves to prevent contact of the skin with the plants. The above-ground non-woody parts are preferably dried in the shade, and should be regularly turned as they do not dry easily.
Diseases and pests
Ruta chalepensis is susceptible to stem and root fungi under humid conditions.
In Ethiopia and South Africa Ruta chalepensis flowers and fruits normally, and is commonly planted in home gardens. Therefore, it is not threatened by genetic erosion. Plants growing at lower altitudes in tropical Africa do not often flower, so the plants are vegetatively multiplied and the genetic variation might therefore be on the low side for these plants.
Ruta chalepensis is popularly used for its medicinal and food flavoring properties. Application of the linear, phototoxic furanocoumarins in medicine as found in Ruta is well documented, for instance in the treatment of psoriasis. Ruta chalepensis therefore merits further research on its potential as a local- or industrial source. However, because of the reported toxic effects, more research is warranted to establish its safety profiles.
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- E.N. Matu, CTMDR/KEMRI, P.O. Box 54840–00200, Nairobi, Kenya
Correct citation of this article
Matu, E.N., 2011. Ruta chalepensis L. In: Schmelzer, G.H. & Gurib-Fakim, A. (Editors). PROTA (Plant Resources of Tropical Africa / Ressources végétales de l’Afrique tropicale), Wageningen, Netherlands. Accessed 9 July 2021.
- See the Prota4U database.