Amorphophallus Blume ex Decaisne
- Protologue: Nouv. Ann. Mus. Hist. nat. Paris 3: 366 (1834).
- Family: Araceae
- Chromosome number: x= 13 (14); A. konjac: 2n= 26 (24, 36, 39); A. muelleri: 3n= 39; A. paeoniifolius: 2n= 26, 28; A. variabilis: 2n= 26
Major species and synonyms
- Amorphophallus konjac Koch, Wochenschr. Gartn. Pflanzenk. 1: 262 (1858). Synonyms: A. rivieri Durieu ex Carriere (1870), Hydrosme rivieri (Durieu ex Carriere) Engler var. konjac (Koch) Engler (1879), Amorphophallus mairei Leveille (1915).
- Amorphophallus muelleri Blume, Rumphia 1: 143 (1837) (" mulleri "). Synonyms: A. blumei (Schott) Engler (1879), A. oncophyllus Prain (1893), A. burmanicus Hook.f. (1893).
- Amorphophallus paeoniifolius (Dennstedt) Nicolson, Taxon 26: 338 (1977). Synonyms: A. campanulatus Decaisne (1834), A. rex Prain (1893), A. gigantiflorus Hayata (1916).
- Amorphophallus variabilis Blume, Rumphia 1: 146 (1837). Synonym: Brachyspatha variabilis (Blume) Schott (1856).
- Amorphophallus, elephant foot yam, sweet yam, konjac (En).
- Amorphophallus, kouniak (Fr).
A. konjac :
- Devil's tongue, konjac (China and Japan), konnyaku (Japan) (En)
- Philippines: pungapung (Tagalog), bulangan (Mangyan)
- Vietnam: khoai nưa.
A. muelleri :
- Indonesia: badur (Javanese), acung (Sundanese), kerubut (Sumatra).
A. paeoniifolius :
- Elephant yam, telinga potato (En)
- Indonesia: suweg (cultivated), walur, eles (wild)
- Malaysia: loki, ubi kekek
- Philippines: pungapung (Tagalog), anto (Bisaya), bagong (Bikol)
- Cambodia: toal
- Laos: duk düa (general), kabuk (southern)
- Thailand: buk (general), buk-khungkhok (south-eastern), man-suran (central)
- Vietnam: khoai nưa, nưa chuông.
A. variabilis :
- Indonesia: cumpleng (Javanese), acung (Sundanese), lorkong (Madurese).
Origin and geographic distribution
The genus Amorphophallus originates from and is mainly distributed in the Old World, especially in the tropics from Africa to the Pacific Islands, but also extending to temperate areas in China and Japan. The genus is not well known, the total number of species is possibly more than 170.
- A. konjac originates from southern and south-eastern China, Vietnam and possibly Laos. It occurs wild and cultivated and easily escapes from cultivation. Its cultivation is most important in China and Japan but it is also known in Indo-China and the Philippines, and occasionally elsewhere (e.g. Hawaii).
- A. muelleri occurs wild from the Andaman Islands eastwards through Burma (Myanmar) into northern Thailand and south-eastwards to Indonesia (Sumatra, Java, Flores and Timor). It is occasionally cultivated (e.g. on Java).
- A. paeoniifolius occurs wild and cultivated from Madagascar eastwards via India and South-East Asia to Polynesia, including also southern China and northern Australia. Because it easily escapes from cultivation and naturalizes, its exact origin is unknown.
- A. variabilis is only known wild in Indonesia (Java, Madura, Kangean Islands).
Tubers from most Amorphophallus species can be made edible in times of food scarcity, usually after peeling, slicing and repeated washing and boiling in water to remove toxic and irritating substances. The remaining flour is used to make a porridge, a type of curd or for making a kind of bread. The 4 species mentioned are also used for food under normal conditions; A. paeoniifolius (important in India, Sri Lanka and parts of Indonesia) and A. konjac (important in China and Japan) in particular are widely cultivated. In Japan, A. konjac tubers are used to prepare a traditional dish ("ito konnyaku") which is gel-like in appearance and texture and is made by adding slaked lime to a colloidal solution of the flour in water, and then heating this. Small one-year-old tubers of A. konjac are considered a delicacy.
The young leaves and the fruits of several species are used as a vegetable. In the Philippines and in India, all parts are also used as fodder. Besides its value as food, the flour prepared from the tubers is also used industrially in China and Japan (e.g. the gluco-mannan in A. konjac has film-forming characteristics useful in preparing stabilizers and emulsifiers for food, drinks, cosmetics and in drilling fluids). The tubers can also be used to prepare acid and alcohol. Many uses of Amorphophallus are reported in traditional medicine: against dysentery, earache, cholera and respiratory problems, to reduce blood pressure and cholesterol level, to cure rheumatic pains and digestive problems. Potentially, all Amorphophallus species can be cultivated as ornamentals.
Production and international trade
Amorphophallus tubers are mainly produced in home gardens or collected from the wild and consumed locally, and only the remainder is available for local trade. No statistics are available for South-East Asia. The often large tubers are easily damaged and are therefore difficult to transport. In China and Japan some A. konjac is cultivated on commercial scale. In China konjac cultivation is about 2000 years old; in 1995 30 000 ha were planted for commercial production. In Japan, production of A. konjac flour increased from 70 000 t per year before 1940 to 130 000 t in 1967 from 17 000 ha. More recent data are not available. Japan also imports tubers from other countries (e.g. from Indonesia; before 1940, especially A. variabilis ), but no statistics are available.
Per 100 g edible portion, tubers of A. paeoniifolius contain approximately: water 75-79 g, protein 1-5 g, fat 0.4-2 g, carbohydrates 18 g (starch 4.5-18 g, sugar 0.1 g, mannan 0-9 g), fibre 0.6 g, Ca 50 mg, P 20 mg, Fe 0.6 mg, vitamin A 434 IU. The energy value is 420 kJ/100 g.
The starch granules vary in shape and size, diameter from 5-19μm.
Per 100 g edible portion tubers of A. konjac contain approximately: water 78.8 g, protein 1.2 g, fat 0.2 g, carbohydrates 19 g, fibre 0.8 g, ash 0.8 g, Ca 43 mg, P 22 mg, Fe 0.6 mg, vitamin A 270 IU. The energy value is about 340 kJ/100 g. The carbohydrates consist of starch, but mainly (more than 50%) of mannan, a polysaccharide of mannose and glucose, which, in combination with water becomes very viscid and is attractive for many industrial processes. The mannan granules are 10-20 times larger than starch granules and are amorphous.
The mannan content of A. muelleri is higher than that of A. variabilis , which is why attempts to exploit the former commercially were made in Indonesia before the Second World War. All species (especially the wild ones) have acrid tubers, due to the presence of calcium oxalate crystals and alkaloids (possibly allied to conicine).
Fresh A. paeoniifolius leaves contain per 100 g approximately: water 85-88 g, protein 2.5-3.5 g, fat 0.4-0.6 g, carbohydrates 2.5-3.5 g, fibre 4-7 g and calcium oxalate 400 mg.
- Perennial herbs with subterranean, naked tubers.
- Tubers often depressed globose and large at maturity.
- Leaves solitary, or several as a result of leaf growth on accessory tubers; petiole cylindrical, solid, usually blotched or flamed, smooth to rough; blade tripartite, each of the 3 segments multifid with decurrent, erect to spreading leaflets (side lobes) which vary greatly in number; just like the tuber, the appertaining leaf becomes larger every year until an inflorescence is formed.
- Inflorescence solitary on the tuber, partly enveloped by a well-developed spathe; peduncle cylindrical, solid, usually blotched or flamed, smooth to rough; spathe seemingly funnel-shaped, tubular or campanulate, but on one side free and with overlapping margins, variously coloured and marked, withering and often falling off after anthesis; spadix female in lower part, becoming male in the upper part via a transitional zone, with a well-developed asexual part (appendix) at the top.
- Flowers unisexual, lacking a perianth; female flowers with 1-4-celled ovary, style more or less absent to well-developed, stigma entire or lobed; male flowers with 1-6 stamens; anthers subsessile and 2-celled, dehiscent by an apical pore; male part and appendix of spadix fall off after anthesis, after which the female part elongates greatly.
- Fruit a 1-3-seeded, subglobose or elongated berry, usually red or orange, the upper ones maturing first.
- A. konjac : tuber up to 30 cm in diameter and 20 cm long, weighing up to 10 kg, brown, seasonally producing numerous rhizomatous offsets; petiole up to 100 cm × 8 cm, smooth or with scattered punctiform warts at the base, dirty whitish-pinkish with large dark green spots and smaller white dots; blade up to 2 m in diameter, highly dissected, rachises narrowly winged; leaflets elliptical, 3-10 cm × 2-6 cm; peduncle up to 110 cm × 5 cm; spathe 10-60 cm × 10-55 cm, limb erect, undulate or folded longitudinally with spreading margins, outside dark purplish-brown with scattered blackish-green spots, inside dark brown, glossy; spadix 15-110 cm long; fruit unknown.
- A. muelleri : tuber up to 28 cm in diameter, weighing up to 3 kg, dark brown outside, yellow inside, developing no seasonal offsets; petiole 40-180 cm × 1-5 cm, smooth, green to brownish-green with numerous pale green spots; blade 75-200 cm in diameter, very dissected, carrying epiphyllar bulbils on the major ramifications; leaflets lanceolate, 10-35 cm × 4-9 cm; peduncle 30-60 cm × 0.5-3 cm; spathe 7.5-27 cm × 6-27 cm, limb semi-erect or spreading, brownish-purple or greyish-green outside, inside purplish or brownish with greenish or brownish spots; spadix longer than spathe, 8-30 cm long; berry cylindrical to ovoid, 12-18 mm long, bright red, up to 1000 per infructescence, 2-3-seeded.
- A. paeoniifolius : tuber up to 30 cm in diameter and 20 cm long, weighing up to 25 kg, dark brown, producing seasonal rhizomatous offsets up to 10 cm × 4 cm; petiole up to 200 cm × 20 cm, shallowly corrugate to strongly echinate-verrucate, pale to dark green with numerous pale blotches and small dark dots; blade up to 3 m in diameter, highly dissected, rachises winged; leaflets rounded-ovate to lanceolate, 3-35 cm × 2-12 cm; peduncle 3-20 cm × 1-8 cm, elongating to 1 m length in fruiting; spathe 10-40 cm × 15-60 cm, limb spreading and strongly undulating, pale green to dark brown with paler spots outside, inside glossy dark brown; spadix shorter or longer than spathe, 7-70 cm long; berry cylindrical, 1.5-2 cm × 8-10 mm, bright red.
- A. variabilis : tuber up to 15 cm in diameter and 8 cm long, weighing up to 1.5 kg, white, producing seasonal rhizomatous, spindle-shaped offsets 1-1.5 cm long; sometimes 2 leaves are produced; petiole up to 120 cm × 3.5 cm, smooth, pure green or variegated green-brown-green; blade up to 125 cm in diameter, rachises narrowly winged; leaflets elliptical to lanceolate, 4-34 cm × 2-12 cm; peduncle 8-120 cm × 0.4-3 cm; spathe 6-23 cm × 5-20 cm, limb strongly reflexed at margin, green with black dots outside, creamy white to pale green or brown inside; spadix usually much longer than spathe, 9-58 cm long; berry orange-red, 1-3-seeded.
Growth and development
For A. muelleri the development on Java is as follows. In November (beginning of the rainy season), the subterranean tuber starts developing one leaf which exhausts the reserves of the tuber completely. During the rainy season a new tuber generally larger than the old one forms at the base of the leaf. At the beginning of the dry season (May-June) the leaf dies and the tuber enters a dormant period lasting 5-6 months. In November, the cycle starts again. When the tuber is large enough (2-3 kg) it develops an inflorescence instead of a leaf. In May, the seeds are ripe but they also remain dormant for 5-6 months. In the next growing season (November-May) the seed develops into a plantlet about 10 cm tall, consisting of one leaf and a subterranean tuber of 1-2 cm in diameter, weighing 5-10 g. The leaf dies in May, the tuber develops a new leaf from November on, reaching 30 cm height, bearing some small bulbils, and a new tuber of 8 cm in diameter weighing 300 g. In May the leaf dies. In November, a new leaf up to 1 m tall develops with bulbils about the size of a 1-year-old tuber. Ultimately the new tuber is 20-25 cm in diameter, weighing 2-3 kg. In November the following year the tuber develops an inflorescence. In Thailand (northern latitude), flowering is in May.
A. konjac tubers normally start flowering when 4 years old (in March-April in China). A. paeoniifolius flowers between March and July in India, Thailand, Peninsular Malaysia, the Philippines, Vietnam (northern latitudes) and in November on Java (southern latitude). On Java A. variabilis flowers between June and December and bears fruits from July-January.
Normally, female flowers are receptive only a short time and usually 2 days before the pollen of the same plant is mature. Cross-pollination seems necessary. Nevertheless, in several species seed does not develop or develops only apomictically (e.g. in A. muelleri , A. konjac ). The mannan content of the tubers is highest just before the leaves wither and is independent of the tuber size.
Other botanical information
- A. konjac . Because it has been in cultivation for 2000 years and also naturalizes easily after escaping from cultivation, it is no longer clear which characters belong to the true wild plant. A. konjac can best be subclassified into cultivar groups and cultivars. In China, many landraces exist.
- A. muelleri . There is some confusion about the correct name, because of the poor original type material and description. Its triploid genome points to a recent origin by hybridization or autopolyploidy. This may also explain the apomictic development of the seed, the development of bulbils and the low pollen production.
- A. paeoniifolius . A very variable species, local populations of which haven often been described as new species. It also forms a crop-weed complex, easily escaping from cultivation and naturalizing. The wild and cultivated forms have been described as separate taxa (wild: var. sylvestris Backer, var. paeoniifolius ; cultivated: var. hortensis Backer, var. campanulatus (Decaisne) Sivadasan) but a subclassification into cultivar groups and cultivars seems more appropriate. Many cultivars have been distinguished already.
In China, A. albus Liu & Wei is also cultivated for its edible tuber.
Amorphophallus usually grows in secondary vegetation, in forest margins and thickets, teak forests, village groves, usually under some shade, up to 700(-900) m altitude for A. muelleri , A. paeoniifolius and A. variabilis , up to 2500 m for A. konjac . Shade, up to 50-60%, promotes tuber production. The optimum average temperatures range from 25-35°C for A. muelleri , A. paeoniifolius and A. variabilis , and from 20-25°C for A. konjac , with optimum soil temperatures of 22-30°C.
A. paeoniifolius develops best with an evenly distributed rainfall of 1000-1500 mm during the growing period. Dry conditions stimulate tuber growth. In China, A. konjac develops best when soil moisture is at 75% of the field capacity, preferably dropping to 60% when the tuber is maturing; in Japan it grows in areas with an average rainfall of 1000-1200 mm during the growing season (May-October).
Amorphophallus is found in many different soil types but never under swampy conditions. It prefers well-drained soils with a high humus content. A deep sandy-loamy soil with pH 6-7.5 is favourable; clay soils are unsuitable because they hamper tuber development.
Propagation and planting
Amorphophallus can be propagated from seed, tubers or tuber parts, bulbils (if available) and by tissue culture. Seed propagation is not a normal practice; seed is not always available and moreover it has a dormancy period of 5-6 months. The dormancy of A. muelleri seed can be broken by keeping seed for 6 days in running water. Propagation from tubers or tuber parts is most common. Small tubers or pieces of 2-4-year-old mother tubers, each with one or more apical buds, are preferred. A disadvantage of tuber propagation is that it requires a large amount of tubers (about 25% of the harvest). Bulbils can be planted like small tubers. One hectare of A. muelleri can produce about 50 000 bulbils and 1.8 million seeds (with about 60% germination). Tissue culture is still experimental but promising.
Good soil preparation is beneficial for good growth. Compact soils should be ploughed well and where waterlogging may occur the crop is preferably planted on ridges. Planting holes of 60 cm × 60 cm × 45 cm are recommended, the bottom filled with a mixture of soil, manure and fertilizer. Planting material is sometimes dipped in liquid cow dung and in a solution of disinfectant (e.g. 2% copper sulphate) first. In Indonesia, tubers are also planted upside down to stimulate lateral bud growth. Planting is done at the beginning of the rainy season. Planting distances vary with the plant material used, e.g. seeds at 10 cm, bulbils at 35-70 cm, tubers at 35-90 cm. Normally, tubers become larger at wider spacings, but tuber growth is also influenced by the size of the planting material, water availability and soil fertility.
Most Amorphophallus is planted in home gardens by smallholders and intercropped with numerous other crops. In estate farming, A. paeoniifolius is often planted under betel palm, coconut, banana or coffee, A. konjac is interplanted with grain crops like maize and sorghum, or grown under shade trees (e.g. Paulownia tomentosa (Thunb.) Steud.).
In the growing season the crop is weeded manually, mechanically or sprayed 2-4 times with herbicides. The crop is also earthed up within 1-3 months of planting. In areas without sufficient rainfall, irrigation is sometimes practised. Mulching is recommended (e.g. in Japan for A. konjac 3-10 t mulch of grain straw or wild herbs per ha per season). Recommendations for fertilizer application vary per country and area. In India, for A. paeoniifolius per growing season and per ha, 25 t organic manure, 20 kg N, 40 kg P2O5and 80 kg K2O is recommended at planting, and again 20 kg N after 2-3 months.
Crop rotation is recommended when weeds or diseases become too dominant. In Japan, however, a permanent cropping system for A. konjac exists (called "jinenjo"), in which young and old plants are grown mixed together like a semi-natural vegetation, in which only older tubers are harvested at the end of the growing season and the rest are left in the ground. In this system a minimum input of chemical fertilizers, herbicides and pesticides is combined with large amounts of mulch. In other countries, all tubers are often collected at the end of the season, stored and replanted at the beginning of the new season. It is difficult to mechanize Amorphophallus cultivation because the tubers are easily damaged and are then susceptible to diseases.
Diseases and pests
In general, no serious diseases and pests are known for Amorphophallus . Reported diseases are: footrot, caused by Sclerotium rolfsii , often in badly drained fields; dry rot, caused by Botryodiplodia theobromae , often under hot and humid conditions; white leaf disease; bacterial leaf blight; dasheen mosaic virus; konjac mosaic virus. Reported pests are: Galerucida bicolor (attacking the leaves), Araecerus fasciculatus (attacking the tubers), and various scale insects, caterpillars and nematodes. Remarkably few diseases and pests occur in the semi-natural "jinenjo" cropping system in Japan.
Normally, harvesting occurs at the end of the growing season, when leaves start to wither. Tubers are carefully dug up because damage will facilitate infection by diseases and pests.
In China and Japan, A. konjac cultivated for food is harvested one year after planting, when the tubers are small but sweet and juicy. For industrial purposes the tubers are harvested after 3 years.
A. muelleri propagated from small tubers is harvested 2.5 years after planting, whereas plants raised from bulbils are already harvestable after 1.5 year.
A. paeoniifolius propagated from small tubers can be harvested after 4 growing seasons, whereas plants raised from pieces of 4-year-old tubers are harvestable one year after planting.
Yield data are scarce because most Amorphophallus is harvested from home gardens when needed. Individual A. konjac tubers weigh about 200 g after 1 year, 1-2 kg after 3 years, and can reach 9-13 kg after 4 years. At a planting distance of 70 cm × 70 cm, a 4-year-old crop may produce about 200 t tubers per ha. Yield of dry flour per ha is reported to be about 7.5 t.
Individual A. muelleri tubers may weigh up to 3 kg. At a planting distance of 70 cm × 70 cm, a 3-year-old crop yields about 50 t tubers per ha.
Individual A. paeoniifolius tubers may weigh up to 25 kg, but normally weigh 4-13 kg. Yield per ha depends on various factors, such as the size of the planting material. On average 22.5 t/ha is reported for India under rainfed conditions; with planting material of 500 g, average yield is 30-43 t/ha, with 1000 g 40-45 t/ha, with 4000 g as much as 85 t/ha.
Individual A. variabilis tubers can weigh up to 1.5 kg. At a planting distance of 70 cm × 70 cm a yield of 30 t/ha is theoretically possible.
Handling after harvest
The natural dormancy of Amorphophallus tubers means that they can remain in the field for some months without quality loss. Planting material separated from the harvested product can best be stored under dry, dark and cool (10°C) conditions. Frost and temperatures above 40°C may kill the material.
Harvested tubers are cleaned first by removing earth, roots and leaf parts, then peeled or grated, and the eyes (buds) and any rotten parts removed. Then they are sliced, washed several times and cooked in water, and the starchy substance that settles out is dried, pulverized and sieved, to give a flour that is ready for consumption. Many variants of preparation exist, depending on region and species. For the production of mannan from A. konjac or A. muelleri , sliced tubers are quickly dried first because within 24 hours the gluco-mannan breaks down enzymatically in the presence of moisture. The dried parts are then pulverized carefully, to avoid damaging the mannan particles in the cells. The remaining powder is sieved and winnowed, to leave a yellow-grey sand-like powder, the so-called iles-mannan flour consisting of gluco-mannan particles. Each particle is surrounded by a thin layer which should be removed by careful grinding. The remaining flour can be stored well and is ready for further industrial applications. About 80 kg iles-mannan flour can be obtained from 1 t fresh tubers.
Germplasm collections of Amorphophallus are available in many institutes dealing with tuber crops such as the Research & Development Centre for Biology (Bogor, Indonesia; A. muelleri , A. variabilis ), the Malaysian Agricultural Research & Development Institute (Kuala Lumpur, Malaysia; general collection), the Philippine Root Crop Research & Training Centre (Visayas State College of Agriculture, Baybay, Philippines; A. paeoniifolius ), the Central Tuber Crops Research Institute (Kerala, India; general collection), the Institute of Botany (Kunming, China; A. konjac , general collection), the Gunma Agricultural Experiment Station (Konnyaku Branch, Gunma-ken, Japan; A. konjac ), and Leiden botanical garden (the Netherlands; living plant collection of 120 species).
The agriculturally more important Amorphophallus species are difficult to breed because they are only propagated vegetatively. In India, China and Japan, breeding programmes exist to develop cultivars with a low calcium oxalate content, high mannan content, high yield, and short growing period. Since genetic variability in the existing cultivars and landraces is rather limited, research is also focusing on increasing variability by crossing with wild species.
Although Amorphophallus is rather popular in certain regions in Asia including South-East Asia, it is unlikely to gain more prominence in agriculture. It will remain a relatively important crop in times of food scarcity. The long growing cycle (3-4 years), the relatively large amount of tubers needed as planting material and the difficulty of mechanizing cultivation are serious drawbacks, so easier crops are preferred for research investments.
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P.C.M. Jansen, C. van der Wilk & W.L.A. Hetterscheid