Khat: pharmacognostical aspects

Sections

ABSTRACT
Introduction
Production
Use
Botany and morphology
Shoott
Leaves
Adulterants of khat
Identification of khat
Acknowledgements

Details

Author: Arnold NORDAL
Pages: 51 to 64
Creation Date: 1980/01/01

Khat: pharmacognostical aspects

Arnold NORDAL
Institute of Pharmacy, Department of Pharmacognosy, University of Oslo, Norway

ABSTRACT

A survey was made of the early literature on the production of khat. A botanical and micromorphological examination of 15 samples of Catha edulis was carried out and the findings were compared with data from the earlier literature on the subject. Based on earlier and present observations, the vital organs (leaves, flowers, fruit and seeds) are described, with illustrations, to assist in the identification of khat.

Introduction

Khat is usually described as the young fresh shoots and leaves of Catha edulis Forsk., a species of the plant family Celastraceae. It is also known by various other names, such as chat, gat, Kus-es-Salahin, miraa, tohai and tschat. The dried leaves are known as Abyssinian or Arabian tea [ 1] .

Catha edulis is a shrub or small tree that has been cultivated for centuries. Its original habitat seems to have been the region of Ethiopia, whence it was brought to neighbouring regions. There are records of the use of khat in southern Arabia in the fifteenth century [ 2] . At the present time, Catha edulis grows in the southern part of Arabia and in Africa, where its habitat extends from northern Ethiopia and part of the Sudan as far south as South Africa [ 3] .

Even if most botanists agree that there is only one species of the genus Catha,there may be considerable variations in the general appearance of samples of khat from different regions. There is reason to believe that these variations are due to the cultivation of the plant over the centuries under differing ecological conditions, as well as to local traditions connected with cultivation and harvesting.

Production

In 1900, on the basis of reports by earlier authors, Beitter [ 4] described the cultivation, harvesting and marketing of khat, which was recorded as growing in north-east Africa andsouth-west Arabia between latitudes 18° N and 30° S. The main areas of cultivation were in Ethiopia, particularly in the Harar district, and in Yemen, where it was grown south of Sana'a in the valleys of Upas and Aphis, as well as on the plateaus at altitudes of over 600 m above sea level. Important sites were Djebel Saber and Djebel Reima, where khat was cultivated on terraces, sometimes in conjunction with coffee plantations.

Quoting the observations of P. E. Botta, who travelled in the area in 1837, Beitter reports that khat was cultivated in Yemen from cuttings that were allowed to develop for three years. The shrubs thus produced were then stripped of their leaves, with the exception of those from some side branches, which developed into young shoots in the fourth year. Cut and bundled, these were sold as kat moubarreh, considered to be of inferior quality. The following year, new shoots grew on the branches that had been stripped and these were sold as kat methani, said to be of superior quality. The tree was left for three years and the procedure was repeated. According to Botta, wild-growing khat, known as kat beledi, had stronger effects and was little used.

Beitter also quoted Barbier de Meynard, who, writing in a journal on oriental languages, contended that the variations in the potency of the effects of khat were due to differences in the soil conditions where it was grown. Thus, there were three types of khat: the first had the most marked effects on the brain and could lead to madness, the second was milder and its effects could be compared with those of alcohol, while the third caused only insomnia.

In still another quotation, Beitter recorded that in the Harar district of Ethiopia, khat was cultivated in three ways: as a dwarf plant, an arborescent shrub and a shrubby tree. The dwarf plants, which had a maximum height of 0.4m, had the most tender leaves, with a pleasant sugary taste when fresh. These were the most sought after and the most expensive. In the plants that grew to full height, the leaves were larger and, although they produced the same effects as the smaller leaves, they were less used because of their less pleasant taste.

Peters [ 2] subsequently described the cultivation of khat in the Harar district where it was grown in terraced plantations at an altitude of about 1,800 m above sea level. Coffee trees were interspersed with the khat, and millet was found in the spaces between the trees. Seed was rarely sown and cultivation was mainly from cuttings. After planting, artificial watering was provided for a period of about 40 days. Thereafter, the plants relied entirely on rainfall. The trees were three or four years old before the first crop was taken and thereafter yielded two crops a year. The trees were pruned annually to keep their height to approximately 5 m, as otherwise they would grow to well over 18 m. The older trees from which the main crops were obtained were 20-25 years old. No disease seemed to be known amongst the khat trees on the plantations visited. The khat was picked two or three times a week and sent to the markets in Harar, where it was accepted as fresh for a period of up to four days after picking. The bundles of khat were wrapped first in green, then in dry, banana leaves and their freshness was preserved by occasional moistening with water.

Getahun and Krikorian [ 5] have recently made an important contribution to the knowledge about khat by describing in considerable detail the early history, botany, cultivation, economics and sociological aspects of the use of Catha edulis, with special emphasis on cultural practices in the Harar district of Ethiopia.

Use

Most of the khat produced is used in the fresh state, when it is chewed to obtain stimulating effects. When fresh material is not available, a dried or powdered form of khat may be taken instead. Khat has also been used for certain medical purposes [ 2] , [ 4] and as an adulterant of common tea [ 1] .

The leaves and shoots of Cassinespecies, mainly Cassine capensis L. (also of the family Celastraceae), and the leaves from Maesaspecies have been mentioned as adulterants of khat [4, 6].

Botany and morphology

A review of earlier literature shows that there are reports of thorough investigations on the botany and morphology of khat. There are, however, certain drawbacks in connection with these sources, in that some of them are very difficult to obtain because they are old and rare (for example, Beitter's thesis [ 4] published in 1900), while others are concerned with only a very limited number of samples.

During recent years, intensive investigations on the chemical composition of khat have been carried out at the United Nations Narcotics Laboratory. It was considered of interest to compare the United Nations samples with the descriptions of khat found in the earlier literature. It was also hoped to provide information that would facilitate the identification of the types of khat on the market. An investigation was therefore made of 13 samples provided by the United Nations Narcotics Laboratory plus 3 herbarium specimens from the Botanical Museum of the University of Oslo, which were added for comparative purposes, identified as follows:

Samples from the United Nations Narcotics Laboratory

From the Yemen Arab Republic

  1. Young shoots, 13-15 cm long, bought in Sana'a, May 1974; preserved in 96% ethanol

From Kenya

  1. Dried (pressed) specimens of fresh khat bought at a market in Nairobi, June 1975

  2. Dried (pressed) specimens of shoots, 13-25 cm long, collected at the Meru region, June 1975

  3. Young shoots, 8-13 cm long, collected June 1975; pre-

Samples from the United Nations Narcotics Laboratory (continued)

From Madagascar (collected November 1977)

  1. Type: white. One young shoot with 10 opposite leaves and one shoot with 22 opposite leaves and clusters of fruits with ripe seeds

  2. Type: red. Two young shoots with 8 and 12 alternate leaves

  3. Type: white. One strongly branched shoot with 36 leaves arranged opposite and alternate

  4. Type: red. One shoot with 15 alternate leaves

  5. Type: red. One shoot with 12 alternate leaves of which two are obcordate and rather small (1.5 x 2 cm)

  6. Type: red. Three shoots with alternate leaves

  7. Type: white. Three young shoots, each with 3 alternate leaves

  8. One branched shoot with alternate leaves

  9. One shoot with 8 alternate leaves, one of which is clearly obovate

Samples from the Botanic Museum, University of Oslo

  1. Flowering branches designated "Catha edulis Forsk. No. 1538 (4629). Nyassa Hochland Station Kyimbila, at 1,200 metres above sea-level. Sept. 3, 1912 Mg. A. Stolz"

  2. Flowering branches designated "649 Catha edulis Vohl-Höchst. W. Schimper pl. Abyssin. Ed. II. Hohenach 1952. Prope ascum"

  3. Cassine capensis L.

The investigation showed that most of the morphological elements important for the identification of khat had already been exactly described, although the accompanying illustrations were often inadequate. Therefore, an attempt has been made here to combine new illustrations with descriptions that are strongly influenced by older papers on the subject. A few new findings that seem to be of importance for identification are also described.

Shoott

The samples investigated consisted of young shoots (stems and leaves) and older shoots with leaves, flowers and fruits. The leaves are opposite or alternate in arrangement (figure I). Occasionally, both arrangements are found on the same twig. The shoots sometimes show heterophylly, one or more of the ordinary oval-lanceolate leaves being replaced by smaller, obcordate leaves (figure I b) that may resemble the leaves of Cassine capensis L. (figure VIII). Stipules can often be observed at the base

Figure 1 Shoots with (a) opposite and (b) alternate leaves

Full size image: 119 kB, Figure 1 Shoots with (a) opposite and (b) alternate leaves

Leaves

Macroscopical features

The leaves may vary considerably in their size, shape and colour according to such factors as degree of development and botanical origin. They are simple, 4-11 cm long and 1.8-5 cm wide at the widest part. They have a short, round petiole, 3-7 mm long. As described by Shadan and Shellard [ 7] , the leaves are usually oval-lanceolate in shape with an acute or sometimes slightly acuminate apex and an acute symmetrical base. With the exception of a small portion near the base which is entire, the margin is serrate, showing 25-30 blunt teeth. The upper surface shows pinnate venation but this is more marked on the lower surface. A few of the lateral veins leave the midrib at a fairly wide angle (45°) but the majority leave at a narrow angle (25-30°) and immediately curve upwards. Near the margin the lateral veins anastomose to form a reticulate

Figure II

(a) Leaf; (b) tooth-shaped projection found in the angles of the serrations

Full size image: 111 kB, Figure II

The youngest leaves are thin and slender. The surface is dull and they have a brownish green colour which darkens upon drying. The adult leaves are bright green, glossy, especially on the upper surface, and have a leathery appearance. The midrib and the most prominent veins on the lower surface may vary in colour from yellow to reddish brown. The distinction of types, such as "white" and "red", is probably connected with this fact (see, for example, samples listed as Nos. 5-11). The leaves are almost odorless and have a slightly astringent taste.

Microscopical features

In the serrate margins of the leaves, tooth-shaped projections are usually, but not always, found in the angles of the serrations (figure II b). The shape and size of these projections vary considerably from one sample of khat to another, and similar bodies are also found on the leaves of other celastraceous plants ( Cassine, Euonymus), as well as on leaves of plants belonging to other families (e.g. the common tea), for which reason they are of limited importance for the identification of khat.

Figure IIIa shows a transverse section of the adult leaf; near the middle part of the lamina; there is little to be found that might form the basis for microscopical identification. The most characteristic feature is the midrib which especially in the lower parts of the leaf, shows a crescent-shaped vascular strand. This can be easily observed in a transverse section of the petiole (figure III, b and c). Cluster crystals of calcium oxalate and cells with black contents (referred to in the older literature as "tanniferous cells") are scattered in the parenchyma. No starch appears to be present. A surface view of the lower epidermis (figure IV a) shows stomata of the ranunculaceous type and cluster crystals which occasionally appear in pairs in the same cell or in two small adjacent cells. Such "twin" crystals, as they have sometimes erroneously been called, have been indicated as a characteristic anatomical feature of khat leav es, but they are hard to find in a microscopical preparation and they may also occur in related species. It is felt, therefore, that they are of little value for identifying khat.

Figure III

(a) Transverse section of an adult leaf; (b) transverse section of the petiole; (c) crescent-shaped vascular strand

Full size image: 112 kB, Figure III

Figure IV b shows a transverse section of the young stem, a few millimetres below the base of two young opposite leaves. The stem is flattened with an elongated great pith and with thin layers of xylem on both sides. Then follow the

Figure IV

(a) Lower epidermis showing stomata and cluster crystals; (b) transverse section of young stem

Full size image: 125 kB, Figure IV

Powdered leaves

The most characteristic elements of the powdered leaves have been described [ 7] as containing fragments of lamina with reticulate venation (figure Ve); fragments of lower epidermis showing stomata surrounded by three or four (occasionally five) cells, some cells containing one or two cluster crystals of calcium oxalate 4- 8 μm in diameter (figure IVa); fragments of upper epidermis with sinuous anticlinal walls (figure Vd); fragments of thick-walled, slightly lignified fibres with lumen of variable width, often obliterated and branched at the ends (figure V, b and c); and fibre tracheids with lignified walls and elongated oval bordered pits (figure Va). Parenchymatous cells with cluster crystals of calcium oxalate (4-40 μm) and parenchymatous cells with dark contents ("tanniferous cells") may also be observed.

The shape and size of the fibres can be easily examined when leaf fragments are subjected to maceration according to Schulze's method [ 8] . In a wide test tube or small vessel 50-100 mg of KClO 3 are moistened with concentrated nitric acid and a few milligrams of small fragments of the leaves are stirred into the mixture, which is heated slightly and stirred until most of the tissue is dissolved. After dilution with water the fibres are studied under the microscope

Figure V

a) Fibre trecheids; (b), and (c) slightly Iignified fibres with lumen of variable width; (d) fragment of upper epidermis; (e) fragment of lamina with reticulate venation

Full size image: 95 kB, Figure V

Flowers

When dried, the flowers are about 2 mm in diameter and dark yellowish brown. A good description of the inflorescence and of the single flowers was given by Christ [ 9] . He reported that the inflorescence of Catha edulis is a short, typical cyme with five or six-fold dichotomy originating from the axil. Sometimes the terminal flower is not fully developed. Each bifurcation is supported by short lanceolate bracts. The flowers, which are on short peduncles, are amongst the smallest within the dicotyledons. They are characterized by a thick, fleshy, hypogenous disc into the margin of which the peripheral parts of the flower are inserted, a common feature of the Celastraceae family (figure VI a). The base of the disc is surrounded by a calyx of five sepals, which are broad-ovate with fimbriate margins. Alternating with the sepals are five oblong-ovate petals of a yellowish white colour, also with somewhat fimbriatc margins. Opposite the sepals are five subulate, lanceolate filaments carrying extremely small tricular anthers

Figure VI

(a) Flower; (b) pollen grain

Full size image: 95 kB, Figure VI

Between the ring of the stamina and the pistil is a green, swollen, broad ring , with five more or less reniform lobes, which are more or less encurved and opposed to the petals, so that the stamens appear to be embedded below the indentations.

A pollen grain with three germ spores is seen in figure VI b.

Fruit and seeds

The following information is taken mainly from Beitter [ 4] , who provided an adequate description of the fruit and seeds.

The fruit has an average length of 8-10 mm (longer ones are also found in Ethiopian plants) and a diameter of 2-3 mm. At the base there is a short stem, 3-8 mm in length, above which is a disc on to which the organs of the flower are inserted, and a somewhat pointed conical capsule, thicker towards the top and flattened (figure VII a). It opens when ripe, with three or four carpels that remain in one piece in the lower half, while the upper half is so that the seeds can escape upwards. The outer surface of the ripe fruit is light-brown, dry and rough. The individual valves are dividedinto two locules by a wall which thickens in the lower half, so that the fruit is actually 6-8 loculate. The separation wall is very thin towards the top, leaving space for two seeds. It is rare for both seeds to mature; usually only two or three seeds develop in the whole fruit. The seeds are small and brown, with a rough, oil-containing testa (in disagreement with Christ [ 9] , who described it as smooth). They are compressed and on one side they have a keel-shaped indentation in which the raphe is placed. The lower tip of the seed is covered by a fine, dry, white, membranous arillus which sometimes grows upwards on both sides of the seed. It is often up to twice as long as the seed itself (figure VII b).

Figure VII

(a) Branch with ripe fruits; (b) seed, outer surface

Full size image: 177 kB, Figure VII

Adulterants of khat

Figure VIII shows a flowering branch of Cassine capensis L. The leaves of this plant are reported to be the most common adulterant for khat. In comparing figure VIII with figure I b it will appear that the normal leaves of the two plants are very different. It is only the obcordate leaves found occasionally in Catha edulis that show a certain resemblance to the leaves of Cassine.

Identification of khat

Khat has very few morphological and anatomical features that would serve as a basis for the purpose of identification. It is therefore strongly recommended that authentic samples of khat should be available for comparative purposes and that identification should be based on more than one method. A combination of methods for the identification of khat has recently been worked out in this laboratory [ 10] .

Acknowledgements

The author is indebted to Dr. O. J. Braenden, the former Chief of the United Nations Narcotics Laboratory, for providing 13 samples of khat that were used in the investigations.

Three herbarium specimens, one of Cassine capensis and two of Catha edulis, were put at the author's disposal by the Botanical Museum of the University of Oslo, and a sample of Euonymus,by the Botanical Garden of the University.

Thanks are also due to Dr. Morten Laane, Botanical Laboratory, University of Oslo, who provided most of the photographs, and to Konsulent I. Gjoen, University of Oslo, who provided a drawing.

Figure VIII

Flowering branch of Cassine capensis L. (about 1:1)

Full size image: 184 kB, Figure VIII

References

001

The British Pharmaceutical Codex ( London, Pharmaceutical Press , 1949).

002

D. W. A. Peters, "Khat: its history, botany, chemistry and toxicology", The Pharmaceutical Journal, vol. 169, 1952, pp. 17-18, 36-37.

003

"The botany and chemistry of khat", Report of an Expert Group, 1979 (MNAR/3/1979).

004

A. Beitter, "Pharmakognostisch-chemische Untersuchung der Catha edulis ", thesis (Strasbourg, 1900).

005

A. Getahun and A. D. Krikorian, "Chat: coffee's rival from Harar, Ethiopia. I. Botany, cultivation and use", Economic Botany, vol. 27, 1973, pp. 353-377.

006

Th. Lasner, in Die natürlichen Pflanzenfamilien III, A. Engler and K. Prautl, eds. (Leipzig, 1896), pp. 214-215.

007

P. Shadan and E. J. Shellard, "An anatomical study of Ethiopian khat (leaf of Catha edulis Forsk.)", Journal of Pharmacy and Pharmacology, vol. 14, 1962, pp. 110-118.

008

E. Strasburger and M. Koernicke, Das botanische Praktikum (Jena, 1923), p. 258.

009

H. Christ, "Über Catha edulis", Archiv der Pharmacie, XX. Jahrgang, 1870, pp. 67-71.

010

A. Nordal and M. M. Laane, "The identification of khat", Meddelelser fra Norsk Farmaceutisk Selskap, vol. 40, 1978, pp. 1 -18.