Difference between revisions of "Catha edulis (PROTA)"

Latest revision as of 13:34, 27 July 2015

Plant Resources of Tropical Africa Introduction

List of species

General importance
Geographic coverage Africa
Geographic coverage World
Stimulant
Medicinal
Timber
Ornamental
Forage / feed
Fibre

distribution in Africa (wild and planted)

1, sterile orthotropic branch; 2, flowering plagiotropic branch; 3, flower; 4, dehisced fruit; 5, seed Redrawn and adapted by W. Wessel-Brand

leafy twigs with flower buds

fruiting branch

mixed cropping of khat and arabica coffee

Catha edulis (Vahl) Forssk. ex Endl.

Protologue: Ench. bot.: 575 (1841).

Family: Celastraceae

Synonyms

• Celastrus edulis Vahl (1790),
• Catha inermis J.F.Gmel. (1791).

Vernacular names

• Khat, qat, kat, Arabian tea, Abyssinian tea, Bushman's tea (En).
• Khat, kat, qat (Fr).
• Katyna (Po).
• Mlonge, miraa, murungu (Sw).

Origin and geographic distribution

Khat is indigenous to the evergreen montane forests in eastern Africa, from Eritrea south to South Africa (Cape Province) and Swaziland. The primary centre of origin is assumed to be in the south-western highlands of Ethiopia. According to 14^th century Arabic chroniclers, khat was cultivated extensively in the mountains of Yemen and also near Harar in Ethiopia at that time. It may have been introduced into Yemen from Ethiopia in the 6^th century AD, some 600 years earlier than coffee (Coffea arabica L.), but was not known to the West until the end of the 18^th century. Its regular use as a stimulant is confined largely to Muslim communities of southern Arabia and eastern Africa. Yemen, Ethiopia and Kenya are the main khat growing countries, but it is also collected from the wild or cultivated in several other eastern and southern African countries and in Madagascar.

Uses

Khat is primarily used as a masticatory. Fresh young leaves, and sometimes the tender shoot tips, are chewed for their stimulating and mildly intoxicating effects. As more leaves are added, a wad is formed which is stored in the cheek. This is slowly chewed until all juices are extracted and the residue is expectorated or swallowed. Chewing is accompanied by drinking large quantities of cold water and sometimes also by smoking cigarettes or water pipe.

Khat chewing is an age-old habit in rural areas to alleviate fatigue during fieldwork or to enliven religious and family gatherings. Occupational groups, such as drivers of motor vehicles, merchants and students, may use it for its energizing effect and to stay awake. In recent years, khat chewing has become a major recreational activity during lengthy social gatherings, particularly in Yemen, Ethiopia, Djibouti and Somalia, resulting in a heavy strain on family incomes and an appreciable loss of productive labour. Rapid transport by air enables regular fresh supplies of khat even to emigrant communities from these countries now resident in Europe and elsewhere in the world.

Larger leaves that are too hard for chewing and leaves that have lost their freshness may be dried and pulverized for the preparation of a paste with water, sugar or honey and sometimes also spices. The paste is chewed and swallowed in a similar manner as described for fresh leaves. Dried leaves are also used to prepare an infusion in the same way as tea, e.g. in South Africa, or they may be smoked liked tobacco, e.g. in Arabic countries. In traditional African and Arabic medicine the leaves and roots of khat are considered a panacea against all sorts of ailments and diseases. When left to grow into large trees, Catha edulis yields a fine timber for furniture and building, called Chirinda redwood in southern Africa. The wood pulp makes excellent blotting paper.

Production and international trade

Recent statistics on cultivation and production are lacking for the major khat producing countries. In northern Yemen khat has overtaken coffee as the most important cash crop; khat production is said to represent about 50% of the gross domestic product of the agricultural sector. Incomes from khat are extremely high; estimates in Yemen range from 5–10 times the income derived from vegetables. It is also a major source of tax revenues for the government. Unlike coffee, there is very little export. It is grown by thousands of small farmers. The popularity of khat chewing has increased tremendously since the 1970s. In Yemen a large proportion of earnings is spent on khat. In Ethiopia, the south-east is the principal region of production with some 10,000 ha, but khat is also grown in several other regions of the highlands. In the mountains near Harer, khat has replaced traditional coffee cultivation to an important extent. Khat often accounts for more than 50% of total cash income of the farmers. Total annual production of khat in Ethiopia was estimated at 50,000 t in 1980. A significant part of the khat sold on local markets in south-eastern Ethiopia is exported by road to neighbouring Djibouti and Somalia, or by air from Dire Dawa to several countries in Africa, the Middle East and to Europe. Miraa, as khat is generally called in Kenya, is cultivated mainly in the Meru District on the north-east slopes of Mount Kenya and in the Nyambeni Hills. Most of it is sold to Muslim inhabitants of the northern and coastal regions, but there is also substantial export by air to major European cities. The importation and trade of khat is formally prohibited in some countries, e.g. Saudi Arabia, the United States, Italy, France and Switzerland, but in many others it is legal or at least tolerated, e.g. most African countries, the United Kingdom and the Netherlands. For instance, 2–3 t of khat bundles arrive in London every week from Ethiopia or Kenya. One small (200–300 g) bundle of khat twigs may sell for US$ 8–20 in the street markets of London, Rome or Amsterdam.

Properties

Young khat leaves have the following approximate chemical composition per 100 g fresh weight: water 90 g, proteins 5–6 g, fibre 2–3 g, tannins (polyphenols) 1.6 g, calcium 0.3 g and ascorbic acid (vitamin C) 0.2 g. They also contain alkaloids of the phenylalkylamine type, including cathinone (= (–)-α-aminopropriophenone), cathine (= norpseudoephredine) and a number of cathedulines, totalling 0.1–0.8% on dry weight basis. Concentrations of alkaloids in older leaves and other plant parts are much lower. Cathinone is the major determinant of the stimulating effects of khat and is ten times more potent than cathine. Cathinone is highly unstable and its content declines to very low levels within a few days after harvesting. This explains the preference of khat chewers for fresh young leaves, perceived quality being closely correlated with cathinone content. Cathedulines do not contribute significantly to the stimulating effects of khat. Cathinone stimulates the central nervous system in a manner similar to amphetamines. Initial effects are elation, alertness, euphoria and lack of fatigue. The large volume of leaves needed for even mildly stimulating effects limits the intake of the active substances and makes khat considerably less dangerous than psychoactive drugs available in a chemically pure form. Generally, only a mild degree of dependence on khat develops. Excessive khat chewing can cause insomnia, lack of appetite (anorexia), hypertension and toxic psychosis, and may contribute to socio-economic problems. The astringent tannins present in khat may lead to gastritis, stomatitis, oesophagitis and periodontitis. The high vitamin C content gives khat leaves some nutritional value. Animal tests showed antispasmodic, analgesic, embryotoxic as well as teratogenic activities of khat. Tests on volunteers who chewed khat on a regular basis showed a significant and progressive rise in blood pressure and heart rate and fall in urine flow rates during a chewing period, and also suggested that khat consumption, especially when accompanied by alcohol and tobacco consumption, might be a potential cause of oral malignancy. The birthweight of children born to khat chewing mothers was significantly lower. Oral administration of the flavonoid fraction isolated from khat produced a significant anti-inflammatory activity against carrageenan-induced paw oedema and cotton pellet granuloma in rats. The wood of large trees is golden-yellow to brown, lustrous, straight grained, fine and even in texture, strong and moderately hard. It saws and planes well. Density of air-dry wood is about 640 kg/m³.

Description

Erect, evergreen, glabrous tree up to 25 m tall with dimorphic branching and a small pointed crown, in cultivation a multi-stemmed shrub (0.5–)2.5–6 m tall; bole straight and slender, up to 20 cm in diameter; bark thin, smooth and pale grey-green in cultivated plants, rough on large trees; branches terete, pale to brownish-grey; young twigs usually flattened, dull green to brownish-red. Leaves alternate on orthotropic and opposite on plagiotropic branches, simple; stipules triangular, 3 cm × 1 mm, pale green, caducous, leaving a rim-like scar; petiole terete, 3–11 mm long, pale to dark green; blade oblong to elliptical or obovate, (3.5–)5.5–11 cm × (1–)1.5–4.5(–6) cm, cuneate to attenuate at base, acute to acuminate, sometimes obtuse at apex, margin glandular crenate-serrate, leathery, glossy, mature leaf leathery, with reticulate venation. Inflorescence an axillary, regularly dichasial cyme up to 2.5(–3.5) cm long, many-flowered; peduncle 6–12 mm long; bracts usually triangular, up to 2.5 mm long, persistent. Flowers bisexual, regular, 5-merous, 2–4 mm in diameter; pedicel 1–2.5 mm long; sepals basally connate, broadly ovate to suborbicular, 0.5–1 mm long, with fimbriate margin; petals free, elliptical-oblong, 1–1.5 mm long, white or pale yellow, with finely serrulate to fimbriate margin; stamens free, alternating with and slightly shorter than petals; disk intrastaminal, fleshy, shallowly 5-lobed; ovary superior, broadly ovoid, 3-celled, styles 3, short, with small stigmas. Fruit a narrowly oblong, trigonous, pendulous capsule 6–12 mm long, red to brown, dehiscing loculicidally with 3 valves, usually 1–3-seeded. Seeds obovoid, flat on one side, 3–3.5 mm × 1.5 mm, with a large membranous wing 5–5.5 mm × 2.5–3 mm; testa dark-brown, rugose-papillose; embryo with two long, thin cotyledons and small plumule embedded in the endosperm.

Other botanical information

The genus Catha consists of one highly polymorphic species. No infraspecific taxa are recognised in Catha edulis, but there are several cultivated forms. In Ethiopia, farmers distinguish several cultivars, including ‘Dallota’ with small pale green leaves, ‘Dimma’ with medium-sized red leaves and ‘Mohedella’ with green to olive-green leaves. In Yemen, khat cultivars are sometimes named after a location, e.g. ‘Sabr’, ‘Reimi’, ‘Taizi’ and ‘Mathani’, or their coloration.

Growth and development

Fresh seeds germinate within 15–20 days. Seeds soon lose viability. Few observations have been published on seedling growth, mainly because nearly all propagation is by cuttings taken from orthotropic (alternate-leaved) shoots. Growth of rooted cuttings starts with the emergence of new orthotropic shoots with reddish bark and alternate leaves from buds above the leaf axils. These stems continue to increase in length for some two years before the first lateral branches with plagiotropic growth appear from the axils of the oldest leaves, bearing slightly smaller opposite leaves. Laterals are progressively formed in most leaf-axils on the vertical stems as these get older. The initial reddish colour of the shoot tips and young leaves turns to green at maturity and eventually greyish-white. Laterals do not branch much, but produce inflorescences in the leaf-axils up to the tip of the branch. The whole growth cycle is repeated when new orthotropic branches start sprouting on 4-year old sections of existing vertical stems. Suckers will also develop at the base of stems in response to heavy pruning. Plagiotropic branches are relatively short-lived and are shed within 3–4 years after formation. Flowering generally occurs during the rainy season (July–September in Ethiopia); fruits mature within 4 months after anthesis. Trees raised from cuttings are multi-stemmed right from the start. Wild khat trees have a single bole branching into a number of vertical stems higher up.

Ecology

In Yemen, Ethiopia and Kenya khat is cultivated in the highlands at 1500–2500 m altitude, where average daily temperatures are 16–22°C (range 6–32°C). Annual rainfall requirements are 800–1000 mm over a period of 4–6 months. Frost and high humidity are growth-limiting factors. Khat can be grown in a wide range of moderately acid to alkaline soils, from sandy loams to heavy clays, sufficiently deep and well drained, with a high organic matter content in the topsoil. It is not salt tolerant.

Propagation and planting

Cuttings 30–50 cm long, taken from orthotropic branches or suckers near ground level, are the main source of planting material. Cuttings prepared from plagiotropic branches root poorly and do not produce good plants. Cuttings may be rooted in a nursery, but are often planted directly in the field during the rainy season. One or two cuttings are planted upright in a hole, sometimes on previously prepared parallel ridges. Planting distances on fairly level land or gentle slopes are 1.5–2.5 m in rows 2–2.5 m apart. Narrower spacings are used where plants are grown as low shrubs. In Yemen and south-eastern Ethiopia, khat is mostly cultivated on mountain terraces allowing only one row of trees per terrace. In the absence of regular rainfall, plants are irrigated until well established. Khat is predominantly a smallholder crop; farmers intercrop young khat plants with food crops during the first 5–6 years, after which shade from the trees becomes too heavy for intercropping. A mixed cropping system of a few rows of khat alternated with one or two rows of coffee (Coffea arabica L.) is not uncommon in Ethiopia.

Management

Khat is left to grow undisturbed for 3–4 years, until about 0.8–1 m tall. Maintenance includes weeding and cultivation to keep the soil loose, thereby helping to preserve soil moisture. Most leaves are then removed to induce the development of young shoots for a first light harvest. Normal yield levels are reached at 5–8 years after planting. The height of khat trees is maintained at 2.5–5 m by regular pruning. Trees can be rejuvenated by cutting back all stems close to ground level and allowing emerging suckers to develop into new stems so that plantations can be kept productive for 50–75 years without replanting. Supplementary irrigation during the dry season increases yields substantially and produces a crop in the off-season, when market prices are higher. In Yemen, khat cultivation has expanded into areas receiving only 300–400 mm rainfall. Here it is always irrigated from wells. Nitrogen fertilizers or organic manures increase yields significantly, but khat is hardly ever fertilized by small farmers.

In parts of the Central Highlands of Yemen, such as the plains and valleys around Rada’, khat is grown as a shrub of about 50 cm tall under intensive management with permanent irrigation and regular applications of fertilizer and pesticides. It starts producing about one year after planting.

Diseases and pests

Khat is relatively free from serious diseases. The following minor pathogens have been identified on khat trees around Harer in Ethiopia: powdery mildew (Oidium sp.), black spot (Dillsiella pollaccii), Septoria sp., and stem and twig galls caused by bacterial infections (Diplodia sp. and Pseudomonas savastanoi). Common insect pests on khat in Ethiopia are: the flat-headed borer (Chrysobothris dorsata), the leaf eating weevil (Systates sp.), and caterpillars of the limabean pod borer (Etiella zinckenella) and of Naddiasa concana and Aphilopota panerostigma, that feed on young leaves and stem tips. Farmers generally avoid applying insecticides for fear of killing a beneficial leaf hopper (Empoasca sp.), considered to improve the quality of khat by causing dieback of older shoot tips and so encouraging new shoots to develop. Mole rats (Tachyoryctes sp.) cause occasional damage to the main stems of young trees just below the soil surface.

Harvesting

Young shoots are picked 2–3 times per week during the season. Harvesting is restricted to the early morning to preserve the freshness of the leaves. Young shoots are broken off and trimmed to a length of about 40 cm, sometimes to 80–100 cm, before tying into bundles of a size sufficient for two hours of khat chewing. A bundle weighing 500 g will provide enough tender leaves and shoot tips (150 g) for a two-hour session of khat chewing. The more tender and juicy the leaves the easier it is to chew them and the higher the stimulating effect. For that reason a bundle of khat twigs should not be older than 2–3 days after harvesting. When grown as a low shrub in Yemen, only 10 cm long tips of twigs, with about three expanded leaves, are picked and tied into small bundles.

Yield

Khat is often grown for home or local consumption and only harvested when the need arises. Such khat plots are not very productive. In market-oriented khat producing regions of Yemen and Ethiopia, yields can be as high as 2 t of fresh shoots per ha per year for well-managed orchards. Average annual yields in Ethiopia are reported to be 800–1000 kg/ha.

Handling after harvest

Bundles of shoots or leaves are sprinkled with water and wrapped in banana leaves, or those of other plants, to preserve freshness and packed in plastic bags for transport to market. Khat arriving early in the morning will fetch the highest prices and will also be fit for export. It is a very perishable commodity; bundles older than 24–36 hours lose their value. Growers, merchants and consumers distinguish several quality grades based on origin, time of harvest, colour and tenderness of leaves. Whitish leaves are considered to be of higher quality, but reddish leaves give a stronger stimulating effect.

Genetic resources

No systematic germplasm collection and preservation programmes exist, but small collections are present in botanic gardens (e.g. at the Agricultural University of Alemaya, Ethiopia). Khat is widespread in its natural habitat in eastern Africa; there appears to be no immediate danger of genetic erosion.

Breeding

There are no formal breeding programmes. Cultivars selected by farmers over long periods of time are maintained by vegetative propagation.

Prospects

Khat will continue to be the preferred stimulant for large sections of local and emigrant populations of South Arabia and East Africa because of its perceived euphoric and strong socializing effects. The demand for this product is, therefore, not likely to decrease in the foreseeable future. High incomes derived from the crop will also guarantee a steady supply to local and overseas markets. When consumed in moderation, khat appears to be fairly harmless and a replacement for alcohol, where this is prohibited for religious reasons. However, long-term health hazards, especially when taken in excessive quantities, require further investigation.

Major references

• Al-Bekari, A.M., Abulaban, F.S., Qureshi, S. & Shah, A.H., 1991. The toxicity of Catha edulis (Khat). A review. Fitoterapia 4: 291–300.

• Geisshüsler, S. & Brenneisen, R., 1987. The content of psychoactive phenylpropyl and phenylpentenyl khatamines in Catha edulis Forssk. Journal of Ethnopharmacology 19: 269–277.

• Getahun, A. & Krikorian, A.D., 1973. Chat: coffee’s rival from Harar, Ethiopia. 1. Botany, cultivation and use. Economic Botany 27: 353–377.

• Greenway, P.J., 1947. Khat. The East African Agricultural Journal 13: 98–102.

• Hill, B.G., 1965. Cat (Catha edulis Forsk). Journal of Ethiopian Studies 3: 18–23.

• Jansen, P.C.M., 1981. Spices, condiments and medicinal plants in Ethiopia, their taxonomy and agricultural significance. Agricultural Research Reports 906. Centre for Agricultural Publishing and Documentation, Wageningen, Netherlands. 327 pp.

• Krikorian, A.D., 1985. Growth mode and leaf arrangement in Catha edulis (Kat). Economic Botany 39(4): 514–521.

• Milich, L. & Al-Sabry, Md., 1995. The case of qat in Yemen. Development 3: 43–46.

• Nencini, P., 1998. Catha edulis Forsk.: ethnopharmacology of a plant with amphetamine-like properties. Fitoterapia 69(5): 13.

• WHO, 1956. Khat. Bulletin of Narcotics 8(4): 6–13.

Other references

• Alles, G.A., Fairchild, M.D. & Jensen, M., 1961. Chemical pharmacology of Catha edulis. Journal of Medicinal and Pharmaceutical Chemistry 3(2): 323–352.

• Dhadphale, M. & Omolo, O.E., 1980. Psychiatric morbidity among khat chewers. East African Medical Journal 65(6): 355–359.

• El Sissi, H.I. & Abd Alla, M.F., 1966. Polyphenolics of the leaves of Catha edulis. Planta Medica 14: 76–83.

• Halbach, H., 1972. Medical aspects of the chewing of khat leaves. Bulletin of the World Health Organization 47: 21–29.

• Kennedy, J.G., Teague, J. & Fairbanks, L., 1980. Qat use in North Yemen and the problem of addiction: a study in medical anthropology. Culture, Medicine and Psychiatry 4: 311–344.

• Kennedy, J.G., Teague, J., Rokaw, W. & Cooney, E., 1983. A medical evaluation of the use of qat in North Yemen. Social Science and Medicine 17(12): 783–793.

• Krikorian, A.D. & Getahun, A., 1973. Chat: coffee’s rival from Harar, Ethiopia. 2. Chemical composition. Economic Botany 27: 378–389.

• Margetts, E., 1967. Miraa and myrrh in East Africa – clinical notes about Catha edulis. Economic Botany 21: 358–362.

• Nencini, P., Grassi, M.C., Botan, A.A., Asseyr, A.F. & Paroli, E., 1989. Khat chewing spread to the Somali community in Rome. Drug and Alcohol Dependence 23: 255–258.

• Nordal, A., 1980. Khat: pharmacognostical aspects. Bulletin of Narcotics 32(3): 51–64.

• Paris, R., 1958. Abyssinian tea (Catha edulis Forssk, Celastraceae): a study of some samples of varying geographical origin. Bulletin of Narcotics 10(2): 29–34.

• Peters, D.W.A., 1952. Khat: its history, botany, chemistry and toxicology. The Pharmaceutical Journal 169: 16–18, 36–37.

• Radt, C., 1971. Contribution à l’histoire ethonobotanique d’une plante stimulante: le Kat. Le Kat en Ethiopie. Revue Ethnographie 65: 38–65.

• Ripani, L., Schiavone, S. & Garofano, L., 1996. GC/MS identification of Catha edulis stimulant-active principles. Forensic Science International 78: 39–46.

• Robson, N.K.B., 1966. Celastraceae (incl. Hippocrateaceae). In: Exell, A.W., Fernandes, A. & Wild, H. (Editors). Flora Zambesiaca. Volume 2, part 2. Crown Agents for Oversea Governments and Administrations, London, United Kingdom. pp. 355–418.

• Robson, N.K.B., 1989. Celastraceae (incl. Hippocrateaceae). In: Hedberg, I. & Edwards, S. (Editors). Flora of Ethiopia. Volume 3. Pittosporaceae to Araliaceae. The National Herbarium, Addis Ababa University, Addis Ababa, Ethiopia and Department of Systematic Botany, Uppsala University, Uppsala, Sweden. pp. 331–347.

• Robson, N.K.B., Hallé, N., Mathew, B. & Blakelock, R., 1994. Celastraceae. In: Polhill, R.M. (Editor). Flora of Tropical East Africa. A.A. Balkema, Rotterdam, Netherlands. 78 pp.

• Rushby, K., 1995. The high life. Geographical, January: 14–17.

• Von Qédan, S., 1972. Catha edulis, eine wenig bekannte Rausch- und Genusdroge. Planta Medica 21: 113–126.

• Zein, Z.A., 1988. Polydrug abuse among Ethiopian university students with particular reference to khat (Catha edulis). Journal of Tropical Medicine and Hygiene 91: 71–75.

Sources of illustration

• Leloup, C.A., 1890. Le Catha edulis. Thèse pour le doctorat en médecine, Faculté de Médecine de Paris. Henri Jouve, Paris, France. p. 6.

• Jansen, P.C.M., 1981. Spices, condiments and medicinal plants in Ethiopia, their taxonomy and agricultural significance. Agricultural Research Reports 906. Centre for Agricultural Publishing and Documentation, Wageningen, Netherlands. 327 pp.

Author(s)

• H.A.M. van der Vossen, Steenuil 18, 1606 CA Venhuizen, Netherlands

Correct citation of this article

van der Vossen, H.A.M., 2002. Catha edulis (Vahl) Forssk. ex Endl. [Internet] Record from PROTA4U. Oyen, L.P.A. & Lemmens, R.H.M.J. (Editors). PROTA (Plant Resources of Tropical Africa / Ressources végétales de l’Afrique tropicale), Wageningen, Netherlands. <http://www.prota4u.org/search.asp>.

Accessed 23 December 2024.

• See the Prota4U database.