Amaranthus spinosus (PROSEA)
- Protologue: Sp. pl. 2: 991 (1753).
- Family: Amaranthaceae
- Chromosome number: 2n= 34
- Spiny amaranth, prickly amaranth, spiny pigweed (En). Epinard malabre (Fr). Brunei: bayam berduri (Malay)
- Indonesia: bayam duri (general), bayem eri (Javanese), senggang cucuk (Sundanese)
- Malaysia: bayam duri, bayam hutan (general)
- Philippines: urai (Tagalog), harum (Bisaya), kalunai (Iloko)
- Cambodia: phti: bânla: (Pursat)
- Laos: hôm hna:m (general)
- Thailand: mang-lang-du (Karen-Mae Hong Son), pa-tue (Khmer), phak hom nam (peninsular)
- Vietnam: rau dền gai (general), giền gai (Ha Nam Ninh).
Origin and geographic distribution
A. spinosus occurs in all tropical and subtropical regions, including the whole of South-East Asia, often gregariously and as a weed. It is sometimes found in temperate zones as well. It has been suggested that spiny amaranth originates from lowland tropical South and Central America, and that it was introduced in other warmer parts of the world from about 1700 AD onwards. Nowadays it is rarely cultivated.
The root of spiny amaranth is known as an effective diuretic. In the Philippines, India, Thailand and Indo-China, a decoction of the root is used to treat gonorrhoea. It is also applied as an emmenagogue and antipyretic. In many countries, including Indonesia, the bruised leaves are applied externally in cases of eczema, burns, wounds and boils. The leaves are considered a good emollient. In Malaysia, spiny amaranth is used as an expectorant and to relieve breathing in acute bronchitis. In mainland South-East Asia, it is also used as a sudorific, febrifuge, antidote to snake poison, galactagogue, and to treat menorrhagia. Spiny amaranth is reported to be used to treat haemorrhoids in Africa. Some tribes in India apply spiny amaranth to induce abortion.
In Indo-China and India, spiny amaranth is used as forage, and it is said to increase the yield of milk in cattle. However, cases of poisoning in cattle have also been reported. Spiny amaranth is browsed by sheep and goats and is a highly nutritious feed at any time during the year. The young leaves are sometimes eaten as a vegetable.
Production and international trade
Spiny amaranth is not traded commercially, and is rarely found in local markets.
Little is known about the specific constituents of A. spinosus . The roots contain α-spinasterol and some saponins. Sterols (β-sitosterol, stigmasterol, campesterol and cholesterol), n-alkanes, fatty acids (e.g. stearic-, oleic- and linoleic acid) and free alcohols have also been found in the petroleum-ether extract of the herb. The flavonoid rutin has been found in the aboveground matter of spiny amaranth in a concentration up to 1.9%, and traces of hydrocyanic acid in the leaves. Spiny amaranth is furthermore reported to contain a considerable amount of potassium, up to 4.5% in the dried leaves, which might explain the known diuretic properties.
A lectin has been purified from the seeds by means of chromatographic procedures. Its reaction was non-specific in general: it reacted with human and various animal erythrocytes. Its unique carbohydrate specificity will prove useful in biochemistry. Lecithins are also known to occur in the seeds of several other Amaranthus species, e.g. A. caudatus L. and A. leucocarpus S.Watson.
Spiny amaranth possesses a strong phagocytic effect. No antibacterial activity has been demonstrated, but crude aqueous extracts showed fungicidal activity against Cercospora cruenta , which causes a leafspot disease in mung bean ( Vigna radiata (L.) Wilczek). However, these extracts were inferior to benomyl in controlling the disease. Furthermore they showed antiviral activity against Aujeszky virus (ADV) in IB-RS-2 pig cell cultures and bovine diarrhoea virus (BVD) in GBK bovine cell lines. The antiviral activity against BVD, however, was lost upon heating the extract for 30 minutes at 50-60°C. Thus it is possible that at least a part of the antiviral activity resides in proteins or glycoproteins that are largely inactivated by heating for 10 minutes above 60°C.
Spiny amaranth has considerable nutritional value. The high foliar content of the amino acid lysine could make it a valuable protein supplement in cereal-based diets. However, cases of spontaneous poisoning by spiny amaranth in cattle have been reported, particularly after severe droughts when few other forages were available. It was suggested that the spiny amaranth caused renal failure.
A. spinosus pollen may cause hay fever, but the reaction is usually milder than that caused by some grass pollen. Hypo-sensitization injection treatment with a mixture of 3 allergenic grasses and spiny amaranth for at least one year gave significant improvement in patients with allergic rhinitis and/or seasonal asthma in the Philippines.
Allelochemicals have been isolated and identified from aerial plant parts. These are volatile aliphatic compounds which inhibit germination of seeds of crops like carrot, tomato and onion. The most active alcohols present in spiny amaranth are 3-methyl-1-butanol and 3-hexen-1-ol; the most active aldehyde is 3-methylbutanal, and the most active ketone is 2-hepatanone.
Adulterations and substitutes
The Amaranthaceae genus Aerva has similar properties to spiny amaranth and is used for similar complaints. It seems probable that Amaranthus and Aerva are related not only botanically but also chemically.
An annual, erect monoecious herb up to 100(-130) cm tall, much branched; stem terete or obtusely angular, glabrous or slightly pubescent, green or variably suffused with purple. Leaves alternate, simple and entire, ovate-lanceolate to rhomboid, 3.5-11 cm × 1-4.5 cm, acute and often slightly decurrent at base, obtuse, rounded or slightly retuse and often short mucronate at apex, glabrous or slightly pubescent on veins when young; petiole rather long, approximately as long as leaf-blade; stipules absent. Inflorescence consisting of dense clusters, lower ones axillary, higher ones often collected in an axillary and terminal spike which is often branched in its lower part; axillary clusters usually armed with (1-)2(-3) very sharp spines up to 2 cm long. Flowers solitary in the axil of a bract, subtended by 2 bracteoles, bracts and bracteoles scarious, mucronate from a broad base, shorter or as long as the perianth, unisexual; male flowers usually arranged in a terminal spike above the base of the inflorescence, green; tepals 5 or in male flowers often 3, free, subequal, ovate-oblong to oblong-spatulate, up to 2.5 mm long, very convex, membranous, with transparent margins and green or purple median band; stamens 5, about as long as tepals; ovary superior, oblong, 1-celled, styles 2-3, ultimately recurved. Fruit an oblong utricle with persisting styles, circumscissile a little below the middle or indehiscent, 1-seeded. Seed about 1 mm in diameter, shiny black or brownish-black with thin margin. Seedling with epigeal germination; cotyledons leafy, glabrous, apex rounded to slightly acute; hypocotyl up to 12 mm long, epicotyl absent.
Growth and development
In India spiny amaranth flowers twice a year. Seeds mature in about one month after flowering. They are scattered around the mother plants or distributed by animals feeding on the plants. It has been observed that large numbers of seedlings emerge from decaying cattle faecal deposits. Seeds are eaten by birds.
In India, seeds germinate throughout the year but seedlings exhibit a high degree of mortality. Less than 1% of them reach the first leaf stage; less than 5% of these reach the 4-leaf stage and continue growing.
Other botanical information
Some other species of the genus Amaranthus (about 40 species worldwide) are also used medicinally, but have other primary uses. The leaves of the well-known vegetable A. tricolor L. are considered as a good emollient in Vietnam, and are used in Malaysia to treat haemorrhagia. The leaves of the lesser-known vegetable A. viridis L. are used in Africa as a febrifuge and as a poultice to treat inflammations, boils and abscesses. In South and Central America, they are used as a diuretic and galactagogue (applied as an infusion) and as emollient. In India, they are used to treat snake bites and scorpion stings, and in New Britain to treat mosquito bites and insect stings. The seeds of the grain amaranth A. cruentus L. are used in India as diuretic and to treat scrofulous sores.
Spiny amaranth is adapted to a wide range of climatic and edaphic factors. It grows best in the sun or in light shade; a light intensity of less than 30% completely suppresses flowering. Flowering is earliest and most abundant in areas with daylengths of 11-12 hours. It is nitrophilous and prefers soils with a high organic matter content, but is also able to grow on sandy soils. Optimal growth is obtained on soils with moderate moisture content, but spiny amaranth is capable of growing on wet soils as well. It is drought-resistant and can even grow under arid conditions.
Spiny amaranth is a very noxious weed in many parts of the world. It is, for instance, troublesome in upland rice, sugar cane and carrot in Indonesia, in maize in the Philippines, in groundnut and soya bean in Taiwan, and in tomato and field pea in India. In South-East Asia, it is very common in roadsides, waste places, railway yards, cropped land and gardens, up to 1400 m altitude.
Propagation and planting
Spiny amaranth is propagated by seed. Some types are known to produce 235 000 seeds per plant. The weight of 100 seeds is 14-25 mg. Freshly collected seeds may germinate at temperatures as high as 40°C, with a germination rate of up to 95%. After storage, however, temperature requirements are lower. Seeds stored for one month at room temperature have almost 100% germination, and after 5 months they have approximately 90% germination. When they are stored for one year at 20°C the germination rate will drop to about 50%, but storage at lower temperatures gives a higher rate.
As a weed in tomato in India spiny amaranth has been successfully controlled by the application of geraniol, which completely blocked the germination of the weed without affecting the the tomato crop. An ethanolic extract of seeds of Coffea arabica L. (with 1,3,7-trimethylxanthine as active ingredient) at a concentration of 1.2 g/l, completely inhibited germination of spiny amaranth in a crop of black gram ( Vigna mungo (L.) Hepper) without negative effects for this pulse crop.
Diseases and pests
Spiny amaranth is a host plant for, among others, tobacco mosaic virus, groundnut rosette virus, cucumber mosaic virus and root-knot nematodes ( Meloidogyne spp.), which attack some commercial crops. When the world's worst weeds are ranked on the basis of the number of pests hosted, spiny amaranth is placed number 6, hosting 15 pests that may affect crops. Some natural insect enemies of spiny amaranth have been recorded from Mexico: the pyralid Herpetogramma bipunctalis and the curculionid Conotrachelus seniculus . These might be useful for biological control. In India, the bud weevil Ceuthorhynchus asperulus , a pest of pigeon pea ( Cajanus cajan (L.) Millsp.), has been found feeding on Amaranthus species including spiny amaranth.
Genetic resources and breeding
The genetic variability of spiny amaranth is great because of its enormous area of distribution and its wide ecological adaptation.
The medicinal properties of spiny amaranth have received very little attention. The diuretic and anti-inflammatory properties in particular deserve more research, as these properties are valued in many different regions of the world. Moreover, the reputed high nutritional value of the leaves offers good prospects for more common use as a vegetable or a forage.
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R.H.M.J. Lemmens & N. Bunyapraphatsara