38

Winged Bean Origins

GRAHAM EAGLETON[1]

February 2002.

The winged bean (Psophocarpus tetragonolobus(L.) DC.) is a leguminous vegetable plant of the humid tropics. Its origins are obscure; while the other eight named species of Psophocarpus DC. are African, the winged bean is essentially a crop of Asia and the Western Pacific.

Two hypotheses have been proposed to explain this anomaly. One supported by much recent taxonomic research, postulates that the progenitor of winged bean arose on the African side of the Indian Ocean whence it was carried East and ennobled through human cultivation. The alternative, implies a wider natural distribution for Psophocarpus, with the winged bean first domesticated within an Indian centre in one model, or within island Southeast Asia and Melanesia in another variation.

This review of literature and of research into genetic variation in the winged bean suggests that the evidence is still insufficient to eliminate either hypothesis, but reveals diverse circumstantial evidence for the antiquity of the domesticate in Asia and Melanesia.

January, 2002.


The winged bean, Psophocarpus tetragonolobus (L.) DC., is a climbing, herbaceous, legume of South and Southeast Asia. While all parts of the plant are edible, throughout most of its distribution it is grown mainly for its green pods and beans (Chandel, Pant, and Arora 1984; Masefield 1973; N.A.S. 1975); a minor vegetable in the household garden complex classified as pekarangan in the terminology (borrowed from Bahasa Indonesia) of Sopher (1980). In Eastern Java and Bali, it is very occasionally grown for its ripe seed, planted in small numbers along the bunds of wet rice fields (sawah in Sopher’s terminology) and consumed in a variety of specialised ways (Sastrapradja and Aminah Lubis 1975). In highland New Guinea, winged bean is a minor field crop, grown for its above ground vegetable parts and for its edible root tubers (Khan, Bohn, and Stephenson 1977) within a high rainfall swidden agricultural system (ladang). In Myanmar, in the plains south of Mandalay, the winged bean is grown without the usual trellis support, on a field crop scale for its salable tubers (Burkill 1906; Eagleton 1999), in a seasonally irrigated dry field system intermediate between sawah and tegalan within Sopher’s schema.

Traditionally, its cultivation has been confined to a broad equatorial belt traversing the Indian Ocean from Mauritius to Melanesia (NAS 1975). Despite this wide and diverse distribution, no evidence for a wild progenitor of the cultivated form of Psophocarpus tetragonolobus has been forthcoming from research within the various countries where it has traditionally been cultivated. Of the other eight named species (plus one unnamed species, reported by Maxted 1990) in the genus Psophocarpus, all are exclusively African, with the exception of P. scandens (Endl.) Verdc. which is also naturally abundant in Madagascar and nearby islands (Verdcourt and Halliday 1978). P. scandens has multiple traditional uses in Africa including as a minor vegetable, and is often planted as a cover crop or companion legume (Harder,Onyembe, and Musasa 1990). It was probably in colonial times, for use as a leguminous cover, that it was carried to India, parts of Southeast Asia and Brazil (Verdcourt and Halliday 1978). There is no clear evidence as to whether it was present outside Africa before colonial times, though this is possible. Prior to the last few years, none of the other Psophocarpus species had been recorded outside Africa.

Although there is no evidence for systematic cultivation of the African species of Psophocarpus species other than P. scandens, Burkill (1906) was drawn by taxonomy to the opinion that cultivated winged bean was likely to have been first domesticated on the western side of the Indian Ocean. In recent years, the view that the ultimate source of Psophocarpus tetragonolobus (L.) DC. is to be found in one of the extant African species has gained support from research (Harder 1996; Harder 1992; Harder,Onyembe, and Musasa 1990; Maxted 1990; Smartt 1980). In the words of Harder and Smartt(1995: 300),this research

“suggests an African progenitor (P. grandiflorus), probably originating in the central African highlands, and subsequent transdomestication to explain the extension of the single cultivated species to its centre of domestication somewhere in Southeast Asia”

In contrast to the African hypothesis, is the Asian hypothesis. On the basis of his observations in Assam, in north eastern India, Vavilov (1951) included winged bean in his Indian centre of crop origins. However, Hymowitz and Boyd (1977) considered New Guinea to be a more likely centre of origin for the winged bean, based on the amount of genetic diversity observed in the Papua New Guinea highlands.

The purpose of this paper, then, is to review the evidence for these models of winged bean’s beginnings and to scrutinise them in the light of research into the structure of the winged bean gene pool.

HISTORY

It has been generally accepted that Georg Eberhard Rumpf's account of Lobus quadrangularis in Amboina (Rumphius 1747) first unequivocally documented the species Psophocarpus tetragonolobus (Verdcourt and Halliday 1978). Rumphius, himself, pointed to possible recordings in the works of Clusius and Plukenet. Clusius (1605) observed the pod of a plant which bore resemblance to P. tetragonolobus but which he described vaguely, such as to leave identification in doubt. In Plukenet's (1696) Almagestum Botanicum, a pod of an “Indian Phaseolus” of the same general form was described under the name Phaseolus indicus with reference to Lobus cartilagineus from the island of Mauritius. However, the diagram in Clusius' work to which Plukenet referred, is of the species Mucuna gigantea (Verdcourt, personal communication); so it is not clear whether Plukenet had seen our particular plant.

Rumphius believed that winged bean had been recently introduced into Amboina, possibly from Java or Bali. Koenig in 1779 saw a "Dolychos with a winged pod" in the gardens around Malacca town (Koenig 1894:104). This "Dolychos" was almost certainly P. tetragonolobus of which there is a lanceolate-leafed form attributed to Koenig in the British Museum (Verdcourt and Halliday 1978). Today the lanceolate-leafed form appears to be absent from the Malacca area, although such types have been observed in the north of peninsular Malaysia (Eagleton,Thurling, and Khan 1978). It is possible that Koenig obtained his specimen in Southern India or Sri Lanka. Chandel, Pant and Arora (1984) have recorded occasional lanceolate-leafed accessions amongst Indian germplasm.

Loureiro recorded winged bean in Southern China in 1790. Burkill (1906) suggested that he was referring to the neighbourhood of Canton although the name (dau roung) that Loureiro (1790) ascribed to the winged bean is Vietnamese rather than Cantonese. There is a herbarium specimen from Yunan province in China (Verdcourt and Halliday, 1978).

In India, winged bean was recorded by Roxburgh (1814). Burkill's argument that it was already in India by 1799, seems persuasive (but see Hymowitz and Boyd, 1977). Certainly by the end of the 19th century its presence had been documented across the breadth of Peninsular India (Graham 1839; Roxburgh 1814; Watt 1894; Wight and Arnott 1834) as well as in Bangladesh, Burma (Wallich 1826), Thailand, Malaysia (Koenig 1894 ), Indochina (Loureiro 1790), Philippines (Blanco 1837), Guam (Anon. 1905), New Guinea (Warburg 1899; Wirz 1924) , Indonesia (Hasskarl 1842; Rumphius 1747) and the Mascarene Islands (Breon 1820). It had not been recorded in the African mainland at that time (Burkill 1906), but has since been widely distributed there (NAS 1975).

GEOGRAPHY

The distribution of winged bean is broadly equatorial (Figure 1). The highest latitudes at which it has been recorded are 210 South in Reunion Island, and 250 North in Assam (Breon 1820; Chandel, Pant, and Arora 1984). It is grown in much of lowland Southeast Asia, but occurs at higher altitudes in Assam, Myanmar and Papua New Guinea, where it has been recorded in cultivation almost to the frost line at 2000 metres (Khan, Bohn, and Stephenson 1977). It has little drought tolerance and requires well-drained moist soils (Duke 1981; Rachie 1977). It has a reputation for survival on "infertile" soils, which is related to its vigorous nodulation capacity (Masefield 1957).

ANTHROPOLOGY

The cultivation of winged bean reaches its most sophisticated level in the highlands of New Guinea. In Mount Hagen (Figure 2), winged bean is the most important legume, and is grown in rotation with the main starch crop, sweet potato (Powell et al. 1975; Powell 1976). It is planted as a field crop with different strategies according to whether it is grown for tubers or for pods (Khan, Bohn, and Stephenson 1977). Although the area of land planted to winged bean per village is rarely more than half a hectare representing less than 20% of available land, at some times of the year tubers can provide more than 25% of the crude protein intake (Stephenson et al. 1979).

Winged bean is grown throughout the highlands of the island, although its importance declines away from the more established agricultural centres. Schumann (1899) recorded winged bean on the north east coast of New Guinea, but the first certain record of the winged bean in the highlands was from the Kremer expedition of 1921-22 (Wirz 1924) which observed cultivation in the Baliem Valley of Irian Jaya. Lam (1945) believed that it had been introduced into the highlands, in the same way as sweet potato, maize and tobacco, which are thought to have arrived less than four centuries ago (Yen 1974). Watson (1965, 1967) on the other hand, suggested that the winged bean might belong with species like yam, taro and Pueraria lobata (Willdenow) Ohwi, to an earlier agricultural phase preceding the introduction of sweet potato.

There has been much debate around the concept of a ‘sweet potato revolution’ in the highlands, and it is instructive to examine winged bean alongside Pueraria lobata, a tuberous legume found throughout Melanesia and Polynesia (Barrau 1958, 1961). Its distribution and use as a starch source prompted Watson (1964) and Barrau (1965) to consider it as a part of an early agricultural phase in the Western Pacific. It is a vigorous (weedy) creeper in secondary scrub, yet its failure to regularly set seed at these equatorial latitudes suggests that its origins are outside Melanesia.

In constrast to P. lobata, the winged bean has not been recorded as an escape in the New Guinea highlands, nor does it appear to have reached Polynesia prior to European intervention in the Pacific (Barrau 1961). It is not likely that the winged bean was grown in the southern part of the New Guinea island before recent times. The main point of comparison between the two leguminous species, is their edible tubers. Yen (1973) has argued that there was no important plant in the pre-European phase of South Pacific agriculture that was reproduced by seed. Winged bean, however, is never propagated other than by seed, so it fits awkwardly into the model of a "pre sweet potato" phase in highland agriculture.

Although in many parts of the Papua New Guinea highlands, tuber production is an important objective of growing winged bean, this is not the case in all parts of the highlands. Clarke (1971) reporting about winged bean in one location in the Western Highlands Province noted:

“In the Ndwimba Basin the leaves and beans are eaten; but the pod is rarely, and the tuberous ‘yam’ never eaten”.

In January 1995, in a survey of five winged bean growing villages in the Baliem Valley of Irian Jaya, the consumption or sale of winged bean tubers were never seen by the current author; no farmer interviewed in this part of the highlands indicated awareness that the tubers can be eaten. On the other hand, pods both in the fresh green stage and in the early ‘bean’ stage, were a daily item in local markets and in the central market at Waimena.

Throughout island Southeast Asia, winged beans are cultivated for pods, and not for tubers. Heyne (1927) noted that apart from Rumphius, no one had recorded winged bean tubers being eaten in Indonesia proper. Root crops do not dominate the subsistence agriculture of Indonesia: cultivated rice was probably part of the diet by 2000 BC (Glover 1977; Glover and Higham 1993). From historical and archaeological records, winged bean seems at no stage to have been more than a minor crop in Indonesia (Sastrapradja and Aminah Lubis 1975). For example, despite its common appearance in the main population centres of Indonesia and Philippines, winged bean seems to be absent or little known in the Toraja areas of central Sulawesi (author’s observations).

It is only in Myanmar that winged bean appears as important as in the New Guinea Highlands, and again, it is mainly for tubers that it is planted (Figure 3). Its cultivation was described in detail by Burkill (1906) and more recently by Eagleton (1999). In Burkill’s time, the most advanced area of tuber cultivation was in Kyaukse, south of Mandalay in the central Burmese plain (Figure 3). He recorded that the seed for these plantings came from the Shan hills at latitudes 200 to 230N. This is still largely the case today.

ARCHAEOLOGY

In 1969, Gorman reported finding carbonised plant fragments of such genera as Cucumis, Lagenaria, Aleurites and possibly certain ‘leguminous’ species amongst archaeological remains dating back to 7000 BC at a cave site in the North West of Thailand 60 km north of Mae Hong Son (Gorman 1969; Solheim 1972; Gorman 1977). It is interesting to note that winged bean is present today in the area of Mae Hong Son (Gypmantasiri and Stern, unpublished survey) and that seed samples, even in the fresh state, can be confused with other legumes e.g. Glycine. However, the preliminary interpretation of the archaeological remains was criticised by Harlan and de Wet (1973). This led to a careful review of the evidence, summarised by Yen (1977). The specimens tentatively identified as ‘leguminous’ remain of doubtful status. Furthermore, in the light of more recent archaeological work, it seems very unlikely that the plant remains found in various ‘Hoabinhian’ sites in North West Thailand were other than those of uncultivated plants left behind by pre-agricultural peoples (Glover and Higham 1993 ; Higham and Maloney 1989 ).