Prota 2: Vegetables/Légumes
Syst. nat. ed. 10, 2: 1269 (1759).
2n = 32, 34
Amaranthus paniculatus L. (1763), Amaranthus sanguineus L. (1763, pro parte), Amaranthus hybridus L. subsp. cruentus (L.) Thell. var. paniculatus (L.) Thell. (1912).
Amaranth, African spinach, Indian spinach (En). Amarante, brède de Malabar (Fr). Amaranto, bredo (Po). Mchicha (Sw).
Origin and geographic distribution
As early as 6000 years ago Amaranthus cruentus was domesticated as a pseudo-cereal (grain amaranth) in Central America from the weed Amaranthus hybridus L. Escaped plants from cultivation also occur in the wild. The vegetable form of Amaranthus cruentus was probably introduced in the tropics and subtropics of the Old World during colonial times. At present Amaranthus cruentus is a widespread traditional vegetable in all countries of tropical Africa. It is the main leafy vegetable in Benin, Togo and Sierra Leone, and very important in many lowland areas e.g. in southern Nigeria, DR Congo, Kenya and Tanzania. It is more popular in humid lowland than in highland or arid areas. It is also an important vegetable in many tropical areas outside Africa e.g. in India, Bangladesh, Sri Lanka and the Caribbean. The Bangladesh type has big fleshy stems, which are consumed with the leaves. Amaranthus cruentus is grown as leaf vegetable throughout South-East Asia, although to a lesser extent than Amaranthus tricolor L. In Indonesia it is grown in mountain areas, where the climate is too cold for the more common Amaranthus tricolor. Grain amaranth, a cultivar-group of Amaranthus cruentus with yellowish white or pale brown seed, is traditionally grown as a cereal crop in Latin America (e.g. Mexico, Guatemala, Ecuador, Colombia). Since colonial times, it has been successfully introduced as a pseudo-cereal in India and Nepal, in mountain areas as well as at lower elevation, and it has become well established as a popular food plant. Thinnings of young seedlings of the grain crop are frequently used as a vegetable. Grain amaranth is produced commercially in hot and dry areas of the United States, Argentina and China. Apart from some try-outs in Zimbabwe, Kenya, Uganda and Ethiopia, grain amaranth is not cultivated in Africa. Ornamental types of Amaranthus cruentus characterized by big bright-red inflorescences can be frequently found in tropical and subtropical countries.
The main use of Amaranthus cruentus is as a leaf vegetable (vegetable amaranth) prepared by cooking and consumed as a vegetable dish or as an ingredient in sauces. The leaves and tender stems are cut and cooked or sometimes fried in oil, and mixed with e.g. meat, fish, cucurbit seeds, groundnut and palm oil. Dishes with amaranth are eaten with the main dish of cereals or tubers. Traditionally in arid regions, the leaves are dried and the leaf powder is used in sauces during the dry season. Experimental work in India and the United States has shown that Amaranthus cruentus is suitable for the processing of leaf protein concentrates, but as far as is known there is no practical application. In colonial times, amaranth was often recommended to Europeans as the best substitute for spinach (Spinacia oleracea L.). In South Africa Amaranthus cruentus is grown commercially for canning and sold in supermarkets.
In Nigeria and Zimbabwe, the introduction of whitish-seeded Amaranthus cruentus cultivars from America as grain amaranth for the improvement of the diet has not been successful. Some people, e.g. in the savanna zone of northern Nigeria, have started to grow the newly introduced seed forms for the leaves.
Forms with large bright red inflorescences are widely grown as ornamentals. A red dye can be obtained from the inflorescences. Amaranthus cruentus is sometimes used as fodder, but only as a moderate part of the daily portion since this use is limited by the high calcium oxalate content. In Benin the dried plants are burned for the preparation of potash. Medicinal uses are manifold. Vegetable amaranths are recommended as a good food with medicinal properties for young children, lactating mothers and for patients with constipation, fever, haemorrhage, anaemia or kidney complaints. Amaranth is rather diuretic. In Senegal the roots are boiled with honey as a laxative for infants. In Ghana the water of macerated plants is used as a wash to treat pains in the limbs. In Ethiopia Amaranthus cruentus is used as a tapeworm-expellent. In Sudan the ash from the stems is used as a wound dressing. In Gabon heated leaves were used on tumours.
Production and international trade
The economic value of Amaranthus cruentus as a popular market vegetable ranks high. From market surveys it appears as one of the main African leafy vegetables, possibly the number one in quantity and area. No statistical data are available, since in most cases all leaf vegetables are recorded as one single group. In national or FAO statistics they are not recorded at all. Correct registration is hampered by the short growing period (3–6 weeks), scattered occurrence of small plots of cultivation, and the dispersed sales in small street markets. In the big cities in Benin the average quantity of fresh leafy vegetables bought daily at the markets was 42 g/head/day, 31% of which was Amaranthus cruentus. There is some unregistered export of amaranth from African countries, as well as from Latin America (Caribbean, Suriname) to Western Europe.
Amaranth leaves have a high content of essential micronutrients. The dry matter content is high (9–22%). The average composition of Amaranthus (probably mainly Amaranthus cruentus) per 100 g edible portion is (averages of about 40 samples): water 84.0 g (78.4–91.3), energy 176 kJ (42 kcal), protein 4.6 g (3.2–6.0), fat 0.2 g (trace–0.6), carbohydrate 8.3 g, fibre 1.8 g (0.4–6.4), Ca 410 mg (69–833), P 103 mg (54–230), Fe 8.9 mg (0.6–10.2), β-carotene 5716 μg, thiamin 0.05 mg (0.05–0.06), riboflavin 0.42 mg (0.36–0.44), niacin 1.2 mg, ascorbic acid 64 mg (52–200) (Leung, W.-T.W., Busson, F. & Jardin, C., 1968). Other analyses indicate that amaranth leaves contain 85 μg folate and 1725 μg carotene per 100 g edible portion. The large variation in moisture content and composition is caused more by variations in plant age and ecological and cultural conditions than by species or cultivar. Compared to other leafy vegetables, amaranth is remarkably rich in vitamin A, vitamin C, iron, calcium and folate. However, the absorption of β-carotene and iron by the human body may be rather low, depending on the quality of the fresh product (age, fertilizer use), the preparation method, the combination with other foods and the physical condition of the consumer. The protein has a high content of sulphur-containing amino acids (methionine, lysine, cysteine), which makes it a good combination with cereals. The leaves easily become soft after 5–10 minutes cooking in lightly salted water. It is not common to add potash. The leaves and stems contain nitrate, mostly in the stems, and also oxalate at a level similar to that of several other green leaf vegetables such as spinach (Spinacia oleracea L.) and spinach beet (Beta vulgaris L.). No adverse nutritional effects occur with a consumption of 100–200 g per day. Moreover, most people cook amaranth in ample water and discard the cooking water containing soluble nitrate and oxalate. A disadvantage of the removal of the cooking water is that water-soluble compounds, especially niacin, riboflavin and thiamin are partly lost. The presence of a rather high content of hydrocyanic acid and oxalic acid makes it less suitable for fresh consumption by humans and as fodder. Their content varies greatly with the cultivar, soil fertility, fertilizer dosage, water supply, and age at harvest. The higher the soil fertility (N, P, K, Ca, etc.), the better the yield and the nutritional composition (especially iron, β-carotene and ascorbic acid). However, excessive N fertilizing may result in an unacceptably high nitrate level.
The composition of grain amaranth per 100 g dry matter (87.7% of the edible portion) is: energy 2006 kJ (479 kcal), protein 14.7 g, fat 8.2 g, carbohydrate 74.2 g, fibre 7.6 g, Ca 282 mg, Fe 3.8 mg, thiamin 0.16 mg, riboflavin 0.36 mg, niacin 1.1 mg, ascorbic acid 0 mg (Leung, W.-T.W., Butrum, R.R. & Chang, F.H., 1972). In Western countries amaranth seed is recommended as a health food. The protein quality is excellent because of the high lysine content (3.2–18%). The oil has antioxidant properties. The starch consists mainly of amylopectin. The very small starch granules make grain amaranth an attractive raw material for industrial uses. The significant amount of squalene (4–11% of the oil portion) means that grain amaranth may find a market niche for industrial production of products such as lubricants in the computer industry and in cosmetics and health foods. The red types contain the red colour amaranthin (α-cyanin).
Adulterations and substitutes
In many dishes where Amaranthus cruentus is used as a green leafy vegetable or pot herb, other amaranth species or other dark green leaf vegetables can be used as a substitute.
Annual herb, erect or less commonly ascending, up to 2 m tall, often reddish tinted throughout; stems stout, branched, angular, glabrous or thinly to moderately furnished with multicellular hairs. Leaves arranged spirally, simple, without stipules, long-petiolate; lamina broadly lanceolate to rhombic-ovate, 2–18 cm × 2–15 cm, attenuate or shortly cuneate at base, obtuse to subacute at apex, mucronate, entire, glabrous to sparsely pilose, pinnately veined. Inflorescence large and complex, consisting of numerous agglomerated cymes arranged in axillary and terminal racemes and spikes, the terminal one up to 45 cm long, usually with many lateral, perpendicular, thin branches; bracts 2–3 mm long, with a long awn. Flowers unisexual, subsessile, with 5 tepals 1–2 mm long; male flowers with 5 stamens c. 1 mm long; female flowers with superior, 1-celled ovary crowned by 3 stigmas. Fruit an obovoid to rhombic capsule 2–2.5 mm long, circumscissile, almost smooth, with a short beak, 1-seeded. Seed obovoid to ellipsoid, compressed, c. 1 mm long, whitish to yellowish or blackish. Seedling with epigeal germination; hypocotyl 10–12 mm long; cotyledons c. 1.5 cm long, fleshy, petiolate.
Other botanical information
Amaranthus comprises about 70 species, of which about 40 are native to the Americas. It includes at least 17 species with edible leaves and 3 grain amaranths. Amaranthus cruentus belongs to both categories.
Amaranthus cruentus is part of the so-called Amaranthus hybridus aggregate, a group of species in which taxonomic problems are far from clarified, especially because of apparently common hybridization and nomenclatural disorder caused by names being commonly misapplied. Some recognized species of this aggregate are cultivated taxa. Amaranthus cruentus is one of these, as are the other grain amaranths, Amaranthus caudatus L. and Amaranthus hypochondriacus L. In fact, a classification in cultivar-groups might be more appropriate for these cultivated taxa.
Amaranthus cruentus seems also closely related to Amaranthus hybridus, a weed that is the putative progenitor of Amaranthus cruentus. Transitional forms between these 4 species can be found. Amaranthus cruentus sometimes escapes from cultivation in ruderal localities.
There are many local cultivars of Amaranthus cruentus propagated and sold as commercial seed. These cultivars are distinguished by plant habit, leaf form and colour, leaf/stem ratio, growing vigour, resistance to fungal diseases, susceptibility to insect attack, drought resistance, photosensitivity, succulence and taste. In some places in East and southern Africa, yellow-seeded grain types introduced from America have mixed and sometimes hybridized with black-seeded vegetable types.
Growth and development
In cool or dark conditions seed remains dormant. Light and high temperatures break the dormancy. In moist soil above 15°C emergence takes place within 3–5 days after sowing. Vegetative development is fast. Like maize and sugar cane, the genus Amaranthus is characterized by the C4-cycle photosynthetic pathway, giving it a high rate of photosynthesis and excellent water use efficiency at high temperatures and radiation intensity. Yet, because of rapid growth, the water consumption is high. A crop with a closed leaf canopy uses about 6 mm/day.
Depending on cultivar, day length and cultural practices, flowering may start 4–8 weeks after sowing, making the plant less suitable for consumption. There are at least four times as many female flowers as male flowers. Pollination is effected by wind, but the abundant pollen production causes a high rate of self-pollination. Some pollination is also effected by insects (bees, flies) and up to 40% outcrossing may occur. Seeds mature after 3–5 months and then the plant dies.
Vegetable amaranths grow well at day temperatures above 25°C and night temperatures not lower than 15°C, but Amaranthus cruentus is grown up to 2000 m altitude in Indonesia. Shade is disadvantageous except in cases of drought stress. Amaranth is a quantitative short-day plant, which is an advantage in the subtropics where the generative stage is retarded during summer. Amaranths like fertile, well-drained soils with a loose structure. The mineral uptake is very high. Although Amaranthus cruentus is fairly tolerant of adverse climate and soil conditions, escapes growing as a weed tend to disappear because they cannot compete with true weeds like Amaranthus spinosus L. or Amaranthus hybridus.
Because of the strong growth of amaranth, weeds are not very troublesome, except nut grass (Cyperus rotundus L.) and weeding is usually not necessary. If rainfall is not sufficient, irrigation by sprinkling should be done before the plants reach their wilting point. Watering every day with 8 mm (8 l/m2) is generally sufficient. Water shortage causes early flowering, which reduces the yield and the market quality. Amaranth is a very high consumer of minerals. On poor soils only modest crops can be grown. The mineral uptake and removal calculated for a crop yielding 25 t/ha is: 125 kg N, 25 kg P, 250 kg K, 75 kg Ca and 40 kg Mg. Larger quantities of N and K are easily absorbed as luxury uptake of these elements is abundant. Much N stimulates vegetative growth and retards flowering. Amaranth responds to high rates of organic fertilizer. In some places it is grown on large quantities (up to 50 t/ha) of almost fresh town refuse, which fulfils its need for minerals. On poor soils, the application of 400 kg/ha of NPK 10–10–20 in addition to 25 t of organic manure is recommended. A split application is recommended during the rainy season. Nitrate-N is better than ammonium-N. Amaranth does not seem to need to be rotated with other crops since no serious soilborne diseases have been observed. Many growers cultivate amaranth continuously on the same beds.
Propagation and planting
Vegetable amaranth is usually grown commercially as a sole crop on beds. It is also found in intercropping systems with food crops and in home gardens. There are 2500–3500 seeds/g. The common cultivation practice is sowing in a nursery at a seed rate of 3–10 g/m2 and transplanting after 2–3 weeks. In this way the grower gets 1000–1500 plantlets per m2 for transplanting. A plant density of up to 180 plants/m2 is often practised for harvesting by uprooting or once-over cutting and gives the highest yield. Higher densities result in self-thinning without yield increase. Field experiments in several countries have shown the advantage of a wider spacing, with about 100 plants/m2, the yield being only slightly lower but the labour requirement for transplanting much lower. During the rainy season very dense planting is applied as a buffer to compensate for heavy plant losses caused by Choanephora stem rot. For repeated cuttings a density of about 20 plants/m2 is appropriate. It is also possible to sow directly, either broadcast or in rows with at least 20 cm between the rows, with a seed rate of 2–5 g/m2. Direct sowing is the common practice in Nigeria, Uganda and in western Kenya. The plants are uprooted after 3–5 weeks. The main advantage is the lower labour costs; however, this method requires more seed, weed competition is more severe and the yield much lower. At harvest, some vigorous plants are left for seed production. For commercial seed production, a distance of 200 m from other Amaranthus cruentus fields is recommended and weedy Amaranthus cruentus or Amaranthus hybridus plants should be removed to avoid outcrossing or mixtures.
Grain amaranths are sown directly and thinned to a spacing of not more than 10 plants/m2..
Diseases and pests
Wet rot or stemrot caused by the fungus Choanephora cucurbitarum is the main disease. It is favoured by wet conditions, poor soil fertility and high nitrogen doses. Spraying with fungicides such as maneb or carbatene reduces the losses, but is seldom applied. Damping-off caused by Pythium aphanidermatum and Rhizoctonia is often serious in seedbeds. It is controlled by good drainage. Over-dense sowing should be avoided. Pythium also attacks older plants. Fungicides such as dithiocarbamates have some effect. Local cultivars show large variation in susceptibility to Choanephora and Pythium. White rust caused by Albugo candida is reported as a minor problem. Alternaria leaf spot has been reported from Tanzania. No virus diseases have been reported.
Insects are a serious problem for amaranth growers. Caterpillars (Spodoptera litura, Helicoverpa armigera, Hymenia recurvalis) and sometimes grasshoppers are the most harmful. The larvae of the stem borer Lixus truncatulus often cause serious damage, sometimes already in the seedbed. The basal part of the plant containing the pupae swells and plant growth is much retarded. Many other insects such as aphids, leafminers, stinkbugs, mole crickets and mites also attack amaranth but generally cause only minor damage. Many commercial growers now spray with insecticides regularly, up to twice a week, instead of using the traditional control method of spreading wood ash to dispel insects. In order to avoid harmful residues, the use of less toxic chemicals is strongly recommended. Biological insecticides derived from Bacillus thuringiensis (Bt) are fairly effective against caterpillars. Amaranth is hardly or not susceptible to nematode damage. Penetrating larvae do not develop further. Moreover, harvesting by uprooting removes Meloidogyne larvae that have penetrated the roots, making the soil more suitable for a next crop of lettuce, okra, African nightshades (Solanum species), Corchorus or other vegetables susceptible to root-knot nematodes.
The optimal harvest period is reached when the total leaf area is 7 times the ground area (LAI = 7). In practice harvesting is done at a younger stage to obtain a more tender product. Most commercial amaranth growers harvest the whole crop by uprooting 20–30 days after transplanting. Some growers harvest by cutting at ground level. If wide spacing is practised, the harvest method is by repeated cuttings, the first cutting about one month after transplanting, and then every 2–3 weeks for a period of one to two months. Cutting is done at a height which leaves at least 2 leaves and buds behind for regrowth. The height of the first cut is normally 10–15 cm. Low cutting retards bolting. Up to 10 cuttings may be obtained at two-weekly intervals. If the crop was sown directly, the once-over harvest by uprooting or by cutting at ground level may be done 3–4 weeks after sowing. Some growers obtain a second harvest three weeks later from the regrowth of the smallest plants.
Grain amaranths, if grown on a small scale, are harvested by cutting the seed heads early in the morning to avoid scattering.
Good growers normally harvest 2–2.5 kg/m2 (maximum 3.0 kg/m2) of an uprooted crop (dry matter content 16%, edible portion 35–50%, being the total of leaves and young stems). The first cutting of a ratooned crop yields 1.0–1.5 kg/m2 (edible portion 70–80%), the following cutting 0.5–1.0 kg/m2. Continuous cropping of amaranth may yield up to 30 kg/m2 marketable product per year. With a land use of 70%, an annual yield of 210 t/ha of marketable product may be obtained. The seed yield of vegetable amaranths is up to 2 t/ha, of grain types up to 5 t/ha. Forage yields of 30 t/ha (with 18% dry matter content) in 8 weeks have been reported, representing a yield of 1.6 t/ha of pure leaf protein of excellent quality.
Handling after harvest
The harvested plants are bundled, the roots are washed and the produce is packed for transport to the market. In markets and shops it is sprinkled with water to keep a fresh appearance. If uprooted, the vegetable can be kept fresh for some days by putting it in a basin with the roots in the water. It is sold in bunches or by weight. The harvested product can be dried in the sun for the preparation of leaf powder. Dry inflorescences harvested for the seed are threshed by putting them in big jute bags and beating with sticks. The bulk of the straw is removed first and then the finer chaff is winnowed.
A collection of amaranths is kept at the Rodale Organic Gardening and Farming Research Center (OGFRC) at Kutztown, Pennsylvania, United States; South-East Asian accessions are kept at the Asian Vegetable Research and Development Center (AVRDC) at Tainan, Taiwan. African cultivars and introductions from OGFRC are kept at the National Horticultural Research Institute (NHR) in Nigeria and African cultivars at the AVRDC centre at Arusha, Tanzania. Indian collections are kept at the National Bureau of Plant Genetic Resources (NBPGR), New Delhi (India). Many national institutes have small working collections of local cultivars. Evaluation and variability studies are needed to reveal the amount of exploitable genetic variation.
Breeding of Amaranthus cruentus as a leafy vegetable has been limited to selection of local cultivars. In some countries (Benin, Nigeria) selections have been made from landraces. A popular and productive cultivar is ‘Fotete’ in Benin. Experimental breeding of grain types in India shows that there are possibilities for improvement by hybridization. A lot of breeding work has been performed on grain types in the United States and India.
Amaranthus cruentus is recognized as an easy-to-grow and extremely productive and nutritious vegetable. It is probably the highest-yielding leaf vegetable of the tropics. It has high potential for the production of leaf protein concentrates. Its excellent nutritional value makes it an important vegetable for human nutrition, both in rural areas for home consumption and as a cheap green vegetable in city markets. Research should focus on the optimization of cultural practices (integrated pest management to avoid pesticide residues, plant nutrition) and on breeding for fungus and insect resistance. Grain amaranth, however, does not have much future in Africa, since it cannot compete with more productive traditional cereals that are easier to grow. Ornamental types of Amaranthus cruentus will probably remain popular garden plants, without much commercial interest.
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Correct citation of this article:
Grubben, G.J.H., 2004. Amaranthus cruentus L. In: Grubben, G.J.H. & Denton, O.A. (Editors). PROTA 2: Vegetables/Légumes. [CD-Rom]. PROTA, Wageningen, Netherlands.
wild and planted
1, part of branch with axillary shoots; 2, leaf; 3, inflorescence; 4, cyme; 5, male flower (one tepal removed); 6, fruit; 7, seed.
crop ready for harvest
field for seed production
amaranth for sale on a market in Sierra Leone