Economic Botany ofSphenostylis (Leguminosae)

ECONOMIC BOTANY OF SPHENOSTYLIS (LEGUMINOSAE) l

D A N I E L P O T T E R

Potter, Daniel (L. H. Bailey Hortorium, Cornell University, Ithaca, New York 14853). ECONOMlC BOTANY OF SPHENOSTrLIS (LEGUM1NOSAE). Economic Botany 46(3):262-275. 1992. Spheno- stylis, a genus of seven species in tropical and southern Africa, includes three taxa that are used by humans. Flowers and seeds of S. schweinfurthii Harms are occasionally eaten in West Africa, and this species has potential value as a forage crop. Flowers and seeds of Sphenostylis erecta (E. G. Baker) E. G. Baker subsp, erecta are eaten in parts of Central Africa, while the roots are used medicinally and as a source of dye and fish poison. The edible tubers of S. stenocarpa (Hochst. ex A. Rich.) Harms, the African yam bean, are collected from the wild in Central and East Africa. This species is cultivated for its edible seeds in west tropical Africa and for its edible tubers in Zaire. Cultivated races of S. stenocarpa may be considered domesticated forms, since they differ from wild plants of the species in a number of morphological characteristics that are evidently the result of human selection. A list of common names for the three taxa, from throughout their ranges, is presented.

La botanica economica de Sphenostylis (Leguminosae). Sphenostylis, un g~nero con siete especies de las regiones sur y tropical de Africa, incluye tres taxa utilizados pot humanos. Las flores y semillas de S. schweinfurthii Harms son alimento ocasional en el oeste de Africa, y la especie tiene, ademas, valor potencial como forraje. Las flores y semillas de Sphenostylis erecta (E. G. Baker) E. G. Baker subsp, erecta se corned en regiones del centro de Africa, mientras que las farces tienen usos medicinales y son fuente de colorantes y embarbascantes. Los tub~rculos comestibles de S. stenocarpa (Hochst. ex A. Rich.) Harms, la ficama Africana, se colectan de plantas silvestres en el centro y este de Africa. Esta especie se cultiva por sus semillas comestibles en el oeste de Africa tropical, y pot sus tub~rculos comestibles en Zaire. Las razas cultivadas de S. stenocarpa pueden set consideradas como formas domesticadas, puesto que differeD de las plantas silvestres en muchas caracterfsticas morfolrgicas que son, evidentemente, el resultado de la selecci6n humana. Se presenta una lista de los hombres comunes para los tres taxa a lo largo de sus rangos de distribuci6n.

Key Words: African yam bean, Sphenostylis, tubers, seeds.

Sphenostylis E. Meyer (Leguminosae: Papili- onoideae: Phaseoleae) comprises seven species that occur in dry forests and in open or forested savannas in tropical and southern Africa. The genus includes sparsely pubescent prostrate, twining, or erect herbs and subshrubs that per- ennate by thickened fibrous or starchy rootstocks. In the shrubby taxa, the stems also persist through the dry season, but the leaves are shed. The leaves are trifoliolate and petiolate with stip- ules and stipels. The inflorescence is an axillary nodose pseudoraceme, bearing two to many ped- icellate bracteolate flowers with showy purple or

Received 23 September 1991; accepted 20 March 1992.

yellow corollas. The woody linear legumes are laterally compressed and ridged along the mar- gins. The most distinctive feature o f Sphenostylis and its sister-genus Nesphostylis Verdc. is the style, which is terete at the base, then flattened and broadened apically, forming a spoon-shaped expansion in Sphenostylis. Sphenostylis and Nes- phostylis are distinguished due to the absence, in Sphenostylis, of standard petal appendages, of apically dilated stamens, and o f a tooth on the vexillary stamen (Verdcourt 1970; Potter 1991).

As part of a systematic study of Sphenostylis and Nesphostylis (Potter 1991), a imed at clari- fying taxonomic boundaries and phylogenetic relationships in the genera and at examining the origins of wild and cult ivated races of S. stenocarpa, an investigation of the uses of the three

Economic Botany 46(3) pp. 262-275. 1992 �9 1992, by The New York Botanical Garden, Bronx, NY 10458 U.S.A.

1992] POTTER: SPHENOSTYLIS 263

economically significant taxa in Sphenostylis was undertaken. The results of that investigation are presented here. The accompanying paper (Potter and Doyle 1992) discusses molecular and morphological evidence concerning evolution within S. stenocarpa.

SOURCES OF INFORMATION

This paper summarizes reports in the literature, information from herbar ium specimens, personal communicat ions from African agron- omists and botanists, interviews with farmers, and observations made during three collecting trips to tropical Africa. Between January, 1986 and July, 1988, collections were made in the Ni- gerian states o f Oyo, Kwara, Niger, Anambra , Imo, Rivers, Bendel, Plateau, and Kaduna, areas of Cameroon, Kenya, Tanzania, Zambia, Zim- babwe, Malawi, and the provinces of Kinshasa, Bas-Zaire, and Shaba, Zaire. In sites where one or more of the economically important taxa of Sphenostylis were found wild or in cultivation, inhabitants of nearby villages who grew and/or used the plants were interviewed, sometimes with the help o f an interpreter, and seeds were collected. Interviews were used to gather information on uses o f the plants, cult ivation practices, and common names. A list of the common names for all three taxa, compiled from a variety of sources and arranged by language group according to the classification system of Fivaz and Scott (1977), is presented in Table 1.

USES OF SPHENOSTYLIS

SPHENOSTYLIS SCHWEINFURTHII HARMS

This species includes erect shrubs found in open savanna areas. The leaflets are oblong. The inflorescence is a lax pseudoraceme with two to four yellow flowers per inflorescence (Fig. 1).

Sphenostylis schweinfurthii, first described from Djurland (southwestern Sudan) and northern Cameroon (Harms 1899) is distr ibuted throughout the Guinea savanna of west tropical Africa from Ivory Coast through northern Ghana, Ni- geria, and Cameroon eastward to Sudan and Ethiopia (Fig. 2).

There are reports in the literature (Dalziel 1937) and on herbarium specimens (e.g., Binga s.n. K; Dent Young 76 K) that the seeds and less com- monly the flowers of this species are eaten in t imes o f hunger. Harms (1911) reported that, according to Kersting, the young flowers of S.

schweinfurthii make a delicious vegetable, "ap- preciated even by Europeans" (trans. Dalziel 1937). Near Ngaoundere, Cameroon and Zaria, Nigeria, where I collected this species, local people were not familiar with these uses.

At Shika, Nigeria in prel iminary studies of the use of legumes native to West Africa as forage crops (Asare et al. 1984), S. schweinfurthii was found to be a promising species in terms o f pal- atabili ty to cattle, although yields were low. Stud- ies are continuing on the value of this plant at the National Animal Production Research In- stitute at Shika (N.A.P.R.I. staff, pets. comm.).

SeHeNOSTYLIS eRECrA (E. G . BAKER) E. G . BAKER SUBSP. ERECTA

This taxon, closely related to the previous one (Potter 1991), is s imilar in habit and general ap- pearance, but has broader, ovate or elliptic leaflets, usually longer peduncles, and subcapitate pseudoracemes with up to ten or more yellow flowers tightly clustered at the apex of each inflorescence (Fig. 3). The long, thickened, fibrous roots produce a red exudate. In this taxon, unlike all others in the genus, flowers are often produced on old shoots before new leaves appear. It is found in woodland savanna, dry forests, along roadsides, and in old cult ivated fields, and is distr ibuted throughout central, east, and southern tropical Africa, from Angola eastward through southern Zaire and throughout Zambia to Tan- zania, and southward to Mozambique, Malawi, and Zimbabwe (Fig. 2).

Sphenostylis erecta subsp, erecta is not cultivated, but several uses of the wild plants are known. In the Copperbelt Province of Zambia and in Shaba, Zaire, members of the Bemba tribe use the roots as a source off ish poison. The sur- faces o f the roots are scraped and the scrapings are thrown into ponds to stun fish. These people use the same roots medicinally: an infusion is made by soaking the roots in water until it turns red; salt is added, and this is imbibed as a treatment for diarrhea. The flowers are also eaten, raw or cooked. Green or mature pods are cooked and the seeds removed and eaten. Wil l iamson (1955) reported the following uses for S. erecta subsp, erecta in Malawi: the flowers and some- t imes the leaves are cooked and eaten, often mixed with the flowers of Dolichos buchananii Harms; the seeds have been eaten in t imes of hunger; the red exudate from the roots is used to mend cracks in pots, to paint them, and to

264 ECONOMIC BOTANY [VOL. 46

TABLE | . C O M M O N NAMES FOR SPECIES OF SPHENOSTYLIS, PRESENTED IN THE FOLLOWING FORMAT:

SPECIES: L A N G U A G E FAMILY, Language Group, [Language]/name/Country-Region/(Reference).

S. schweinfurthii: AFRO-ASIATIC, Chadic, Western Group, [Hausa]/waken kurege, waken bareyi/Nigeria/ (Dalziel 1937)

S. erecta ssp. erecta: CONGO-KORDOFANIAN, Niger-Congo, Bantu, Nyanja group, [ciCewa]/nkjunga/ Malawi/(Williamson 1955); [ciNyanja]/nkhunga/Malawi/(I. H. Patel, pers. comm.); [ciNyanja]/mlnli (flowers)/ Malawi/(Williamson 1955); Yao group, [ciYao]/ngunga/Malawi/(Williamson 1955); Luba group, [kiLuba]/chilu- lungkundja/Zaire (Shaba)/(pers. obs.); [kiLuba]/muputu/Zaire/(Wilczek 1954); Luba group, [?]/kafulo/Zaire (Sha- ba)/(Wilczek 1954); Bemba group, [kiTabwa]/mukunde kunde, mukundiaJZaire/(Wilczek 1954); [kiBemba]/ kimambaJZaire (Shaba)/(pers. obs.); Language group unknown, [?]/munkoio/Zaire (Karavia)/(Wilczek 1954); [?]/ kafulo/Zaire (Shaba)/(Wilczek 1954).

S. stenocarpa: AFRO-ASIATIC, Chadic, Western Group, [Hausa]/girigiri, kashin kaji/N. Nigeria/(Dalziel 1937); NILO-SAHARAN, Chaff-Nile, Central Sudanic, Moru-Madi group, [Logo]/arepa/Zaire/(Wiiczek 1954); CONGO-KORDOFANIAN, Niger-Congo, Gur, Moore-Gurma group, [Mossi]/noruko, dieguem tenguere/Fr. Sudan/(Dalziel 1937); [Bassaff]/sesonge, gundosolio/Togo/(Gaisser 1912); [Konkomba]/sumpelegu/Togo/(Gais- ser 1912); [Kabure]/tschangilu kolumo, tschangilu kumaeto, tschangilu kugbaeto/Togo/(Gaisser ! 912); Language group uncertain, [Tschaudjo]/kotonusu/Togo/(Gaisser 1912); Niger-Congo, Kwa, Western Group, [Ewe]/kutreku, kulege/Gahana/(Dalziel 1937); [Twi]/akitereku/Ghana/(Dalziel 1937); [Guan]/apetreku/Ghana/(Dalziel 1937); Yoruba group, [Yoruba]/sese, sese ere; sheshe/S. Nigeria/(Dalziel 1937; pers. obs.); Ibo, [Ibo]/okpodudu; odudu, akedi-wangu, akedi-nwa-ngwu/S. Nigeria/(B. Okigbo, pers. comm.; Dalziel 1937); [Ibo]/azima/S. Nigeria (Imo)/ (pers. obs.); Nupe group, [Ebira]/ikiza/S. Nigeria (Kwara)/(pers. obs.); [Nupe]/shinshere/S. Nigeria/(Dalziel 1937); Niger-Congo, Benue, Bantoid, Tivoid, [Tivi]/ahumaJS. Nigeria/(Dalziel 1937); Language group uncertain, [Be- nin]/khekeh, ihiehle/S. Nigeffa/(Dalziel 1937); [?]/irigiri; akide; iyihe/S. Nigeria (Nsukka; Rivers; Bendel)/(pers. obs.); Niger-Congo, Adamawa-Eastem, Zande group, [Zande]/giliabande/Zaire/(Wilczek 1954); Niger-Congo, Bantu, Bemba group, [kiBemba]/kilumbwelumbwe, malumbwelumbwe/Zaire (Shaba)/(pers. obs.); Lunda group, [Ndembo]/pempo/Zaire/(Wilczek 1954); [Kandembo]/semfu, semvu/Zaire (Shaba)/(pers. obs.); Luba group, [kiSanga]/masemfu, masemvu/Zaire (Shaba)/(pers. obs.); [kiLuba]/tongo ya masemvu; tukunyia masombe/Zaire (Shaba)/(pers. obs.; Wilczek 1954); [Lulua]/kakunde kunde/Zaire/(Wilczek 1954); Duala group, [Kelemba]/ dilomhwe, malubwe/Zaire/(Wilczek 1954); kiKongo group, [Congo]/mfila/Zaire/(Wilczek 1954); Tongwe group, [kiTongwe]/sisebaJTanzania (Mahale)/(pers. obs.); Tumbuka group, [ciTumbuka]/cinkhoma/Malawi/(William- son 1955); Nyauja group, [ciCewa]/nkhoma/Malawi/(Williamson, 1955); Group uncertain, [?]/mfuyu/Zaire (Ban- dundu)/(J. Paulus, pers. comm.); [Mulungu]/tshuku/Zaire/(Wilczek 1954); [Buluba]/djitatu/Zaire/(Wilczek 1954); [?]/mpembo, mpempu/Zaire (Bas-Zaire)/(Wilczek 1954); [Luki]/madeso soto/Zaire/(Wilczek 1954); [Kisa]/masan- gwa/Zaire/(Wilczek 1954); [Mbenge]/nzangi nzangi/Zaire/(Wilczek 1954); [Mayumbe]/madezo soto/Zaire/(Wil- czek 1954); [Bashi]/mulula/Zaire/(Wilczek 1954); [Dolo]/liko/Zaire/(Wilczek 1954)

make them waterproof, and the fibers of the roots are used to make string and mats. Other uses for this plant in Malawi (I. H. Patel, pers. comm.) include the use of the roots for fish poison, as in Zambia, and of their red exudate to decorate large baskets.

SPHENOSTYLIS STENOCARPA (HOCHST. EX A. RICH.) HARMS

The most widely distributed and morpholog- ically variable species in the genus, S. stenocarpa, the African yam bean, is also by far the most important economically. The leaflets may be linear, lanceolate, ovate, or elliptic. The lax pseudoracemes bear from two to twelve purple to magenta flowers (Fig. 4). The flowers of this spe-

cies, unlike the previous two, have twisted standard petals. The plants range from delicate prostrate twiners in some wild populations to robust climbers reaching a height of several meters in some cultivated races. In spite of this variability, cladistic analyses of morphological and chloroplast DNA (cpDNA) data support inclusion of all of these elements in a single species (Potter 1991). The plants develop starchy tubers that serve as organs ofperennation, the above-ground parts of the plants dying back during the dry season. S. stenocarpa is found in open and wood- ed savannas, in forests, on rocks, and both as a weed and a crop in cultivated fields. The species was first described from Ethiopia (Richard 1847) as Dolichos stenocarpus; it was transferred to


Fig. 1. Sphenostylis schweinfurthii, a) Habit, x0.5. b) Leaflet, x0.5. c) Calyx, x 1.3. d) Standard, x0.9. e) Keel, x0.9. I) Wing, x0.9. g) Anthers, x 1.1 h) Gynoecium, • 1.3. i) Seed, x2.0. j) Pod, x0.5.

Sphenostylis by Harms (1899). The African yam bean is distr ibuted throughout most of tropical Africa, from Guinea eastward to Ethiopa, southward to Mozambique and Zimbabwe in the east and to Angola in the west. It is, however, absent from the lowland rainforest of central Zaire (Fig. 5).

Both the seeds and the tubers of S. stenocarpa are edible, and both parts are harvested from

plants in the wild and in cult ivation (Fig. 6). The observation that the distinction between cultivated and wild plants is not always a sharp one (Harlan 1975) applies to S. stenocarpa. Wild plants may be brought into gardens and tended without becoming truly domest icated forms, and domesticates may escape to the wild. Some races ofS . stenocarpa, however, are true cultigens that are propagated by humans while others are strict-


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1992] POTTER: S P H E N O S T Y L I S 267

Fig. 3. Sphenostylis erecta subsp, erecta, a) Habit, • b) Leaf, • c, d) Variation in leaflet shape, • e, t) Calyx, x0.9. g) Standard, • h) Wing, • i) Keel, x0.9. j) Anthers, • k) Gynoecium, x0.9.1) Seed, • 1.7.


Fig. 4. Sphenostylis stenocarpa, a) Habit, x0.5. b) Node, x2. c) Variation in leaflet shape, x0.5. d) Calyx, x0.9. e) Standard, x0.9. t) Wing, x0.9. g) Keel, x0.9. h) Anthers, x0.9. i) Gynoecium, x0.9. j) Pod, x0.5. k) Seed, wild plant, x 2.0. 1) Seed, cultivated plant, x 2.0.


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ly wild, and these two groups may be distinguished not only by the conditions in which they grow but also by a number of morphological changes that typically occur as a result of selection during the process of domestication (Zohary 1984). These include: delayed dehiscence of pods; increased pod size; increased seed size, to a great- er extent in races cultivated for seed than those cultivated for tubers (Potter and Doyle 1992); and increased tuber size, at least in races cultivated for tubers. In addition, the seeds of wild races are covered with black waxy elaborations that form a regular honeycomb-like pattern over the seed surface (also found in some other species in the genus), while seeds of domesticated races are glabrous.

All field collections could be easily designated as domesticated or wild, based on locality of or- igin as well as seed size and surface type. Her- bar ium specimens, most of which lacked seeds, proved more difficult to classify. There was fre- quently no information as to whether they were collected from the wild or from cultivation. A note that part of the plant is edible does not necessarily mean that it was cultivated or even used by local people, and plants apparently in cultivation do not necessarily represent domesticated races. Conversely, even when the descrip- tion of a locality gives the impression that the plants were growing wild, they might have been collected from a formerly cultivated field that was only recently abandoned and allowed to re- vert to forest or bush. Although I found no evidence from my field observations or from ex- aminat ion of herbarium specimens to support reports in the literature (Harms 1911; 1915) that S. stenocarpa has been cultivated in Tanzania, it is possible that cultivation of the plant there did not result in the production of plants with the "domesticated" morphology seen in other areas, or that domesticated plants from that area are not represented in the collections I have seen. Finally, reports of the use of the plants from the wild may have been misconstrued as reports of cultivation.

Will iamson (1955) reported that, in parts of

Malawi, tubers ofS. stenocarpa are collected from the wild, boiled or roasted, and eaten mostly by children but sometimes by adults. Near Mahale Mountains National Park, Tanzania, on the eastern shore of Lake Tanganyika, S. stenocarpa grows wild. A member of the Tongwe tribe living there informed me that when he was young, he and his family collected tubers of this species from the wild and ate them cooked, but that this practice is no longer common. A similar situa- tion exists in Zaire and Congo, where tubers of a narrow-leafleted race of S. stenocarpa are harvested from the wild, cooked, and eaten. This narrow-leafleted plant was described as a sepa- rate species, S. congensis, by Chevalier (1913a), based on material from Brazzaville, Congo, where he observed the consumption of tubers by local people and noted their similarity to S. stenocarpa, which he knew as a plant cultivated in Bas- Zaire. At the village ofMenkao, Zaire, about 100 km NE of Kinshasa, I observed plants of this type growing wild in old cassava fields adjacent to fields where plants of a domesticated race of S. stenocarpa were cultivated. The narrow-leafleted wild plants are known locally as " 'mpempo" or "pempo," the same name applied to cultivated plants of this species in Bas-Zaire. The cultivated race in Menkao is called "mfuyu," the name used in Bandundu Province, where, I was told, the plants cultivated at Menkao had orig- inated. My conversations with people at Menkao indicated that they recognized the close relation- ship between the wild and cultivated races of S. stenocarpa. I was told that the tubers of both have a good flavor, but that the cultivated variety is preferred because tubers of the wild plants cause sore throats and headaches.

Within Zaire, the major areas of cultivation of S. stenocarpa are in the provinces of Bas-Zaire, Kinshasa , B a n d u n d u , and Shaba (Fig. 6). Throughout these areas, the tuber is the most valued part of the plant, although, in at least some villages in Bas-Zaire, the seeds are sometimes consumed. The tubers are boiled and eaten plain or in stews, and the flavor, similar to that of the potato (Solanurn tuberosum L.), is highly

Fig. 6. Map showing utilization of Sphenostylis stenocarpa and ecological zones in tropical Africa. Stars = collected from wild for consumption of tubers and/or seeds. Solid squares = cultivated for tubers. Solid circles = cultivated for seeds. Horizontal lines -- desert and dry steppe; white = savana and dry woodland; dots = tropical rainforest. After Murdock 1959.

1992] POTTER: S P H E N O S T Y L I S 271

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esteemed. African yam bean is grown as an annual crop. The plants are usually propagated by seeds, which are planted in September or Oc- tober. The tubers take seven to eight months to mature and are harvested in May to July. They are often grown in cassava (Manihot esculenta Crantz) fields, the bean stems twining around those o f the cassava plants. Other crops, such as maize (Zea mays L.) and sweet potatoes (Ipomea batatas (L.) Lam.), may be present in the same fields. According to people who grow them in Shaba, seeds are extensively dispersed by people, at least within tribal boundaries. In Shaba, Zaire, where S. stenocarpa is cultivated and S. erecta subsp, erecta is collected from the wild, a rela- t ionship between the species is recognized by local people. This is reflected in the similari ty of some common names for the two plants (Table 1). For example, "mukunde kunde" is the name for S. erecta in kiTabwa and "kakunde kunde" the name for S. stenocarpa in Lulua (Wilczek 1954).

In West Africa, S. stenocarpa is cultivated in a number o f countries including Togo and Gha- na, and most extensively in Nigeria, where it is grown as a crop plant in both the savanna and the forest zones (Fig. 6), in the following states (Ezueh 1984; B. N. Okigbo, pers. comm.): Oyo, Kwara, Niger, Benue, Anambra , Imo, Rivers, Cross River, Bendel, and Ondo. My own obser- vat ions and discussions with people in Nigeria and Ghana indicate that, at least now and in the recent past, the plant has been grown only for consumption of the seeds in those countries. While people in at least some of the areas I vis- i ted in Nigeria are aware that the plants produce tubers, they do not eat them. There are, however, several reports in the literature of the use of the tubers in West Africa (Harms 1911; Rachie and Roberts 1974). According to Gaisser (1912), both tubers and seeds were eaten in Togo, but the tube r s were d i s d a i n e d by m e m b e r s o f the Tschaudjo tribe. It is interesting to note that one of the names applied to S. stenocarpa in Mossi (spoken in West Africa) is "dieguem tenguere," which means "producing its young in the ground" (Chevalier 1913b). According to Dalziel (1937), however, this name is properly applied to the geocarpic Macrotyloma geocarpum (Harms) Ma- rechal & Baudet; its use for the African yam bean may indicate recognition o f morphological similarity between the two plants, rather than aware- ness that S. stenocarpa can reproduce by tubers.

As with the cult ivation o f this species in East Africa, it is possible that use of tubers in West Africa is a practice that has disappeared within this century or is l imited to very local areas, or that reports of this practice are false. Hypotheses concerning the origins of and relationships among races cult ivated for tubers and races cult ivated for seeds are discussed in the accompanying paper (Potter and Doyle 1992).

In most areas of Nigeria, S. stenocarpa is grown as an annual, but in the village of Nimwoye, Niger State, I was told that the plants came back from rootstocks after the dry season every year, and that a single plant could be mainta ined for more than 20 years. Like the tubers, the seeds take seven or eight months to mature; in Nigeria, they are planted from April to July and harvested in December or January (Ezueh 1984; pers. obs.). African yam bean may be grown in small home gardens for family use or as a crop plant to be sold in markets. It is generally considered to be a minor crop, but in some areas of eastern Ni- geria, it is more important . For example, farmers in Awgu village, Anambra State, and in Uzuakoli village, Imp State, consider the African yam bean an important source o f income, and it is the major legume grown there. In these areas, S. stenocarpa is considered a women's crop, meaning that women have pr imary responsibili ty for its cult ivation and harvest.

In Nigeria, the plants are sometimes grown in fields with cassava and yam (Dioscorea spp.); it is unclear whether the English common name for this crop is based on its association with the latter plant (Ezueh 1984) or on the fact that it produces yam-like tubers, or both. When the three afore- ment ioned plants are grown together, they are planted in the same mounds and the yam bean vines cl imb up the cassava stems. In other villages, both yams and yam beans are planted in fields previously planted to Zea or Sorghum; the vines then climb up the old stalks o f those grains. Other practices include the use of wooden stakes for yam beans and yams, and the use of yam beans climbing on stakes as a fencing around fields ofcocoyam (Colocasia esculenta (L.) Schott or Xanthosoma Schott spp.). Other cultivated plants often found in the same fields include: Telfairia occidentalis Hook. f., Hibiscus sabdarif-

fa L., Abelmoschus esculentus (L.) Moench, Ver- nonia amygdalina Delile, and Solanum spp.

In Nigeria, the seeds of S. stenocarpa may be eaten boiled, after soaking for several hours or


overnight, plain or in stews, or the seed coats may be removed and the seeds ground into a paste with seasonings, which is wrapped in ba- nana leaves and boiled (Ezueh 1984). The seeds may also be eaten fried with or without prior soaking. The unsoaked fried seeds are noted for their sustaining effect; it is said that if a portion of them is taken with water in the morning, one can work all day without any other food (B. N. Okigbo, pers. comm.).

Other uses o f S. stenocarpa were recorded in Togo by Gaisser (1912). The Bassari, he reported, used a paste made from the seeds as a remedy for stomach aches; another variety was said to make people giddy when taken in excess, but a meal made from the seeds mixed with water was said to make drunk people sober (Gaisser 1912; Dalziel 1937). Traditional use of the seeds of S. stenocarpa mixed with water as a treatment for acute drunkenness in West Africa was also reported by Asuzu (1986), who, in studying the effects of aqueous extracts of the seeds in albino mice, found that there may be a pharmacological basis for this traditional practice.

While the seeds o f wild S. stenocarpa are con- sistently dark, either black or mottled with dark brown and black, and those of Central African races cultivated for tubers show a similarly lim- ited range of colors, considerable diversity exists among the races cultivated for seed in West Af- rica. Ezueh (1984) reported a preference for light- er-colored seeds (gray to tan) in northern Nigeria and for dark brown or black seeds in the southern lowland areas. Although none of the farmers I interviewed expressed such preferences, my observations of seeds collected from different parts of Nigeria support this claim. Dark speckled seeds like those of the Central African cultivated races and wild collections and those of the related wild species, S. angustifolia Sonder and S. zimbabwe- ensis Mithen inded., are common in the more southern areas o f Nigeria.

Several studies have been done of the nutritional value o f the tubers (Chevalier 1913b; Okigbo 1973) and seeds (Edem et al. 1990; Evans and Boulter 1974; Okigbo 1973; Onyembe et al. 1982) o f S. stenocarpa. The reported values for total seed protein content vary from 19.5-29% on a dry weight basis, values similar to that reported for cowpea (Vigna unguiculata (L.) Walp.; 24%) hut low compared to those of winged bean (Psophocarpus tetragonolobus (L.) D.C.; 32.8%) and soybean (Glycine max (L.) Merr.; 35.1%)

(Duke 1981). The amino acid composition o f S. stenocarpa, however, is comparable with that of soybean (Onyembe et al. 1982), and the lysine and methionine contents may, on average, be higher (National Academy of Sciences 1979). The major problem with the seeds of S. stenocarpa as a food source is that they require a long cooking time (Okigbo 1973). Trypsin inhibitors present in the seed may be inactivated after only two hours of cooking (Onyembe and Kejuni 1983), and HCN, tannin, and oxalate content were all considerably reduced after overnight soaking and 3 hours o f cooking (Edem et al. 1990). In con- trast, other toxic factors in the seeds that are reported to cause diarrhea may not be completely inactivated until after 12-14 hours of cooking (Asuzu and Undie 1986). The protein content of the tubers of S. stenocarpa (l 1-19% on a dry weight basis), while not as high as some other tuber-producing legumes such as winged bean (20% average), is considerably higher than that of the major root crops grown in tropical Africa, such as cassava (less than 5% protein) and yam (about 6% protein) (National Academy of Sci- ences 1979).

Highest yields of both seeds and tubers of S. stenocarpa are reportedly obtained when it is planted with yams, maize or vegetables (Ezueh 1984; Okigbo 1973), which is the traditional way it is grown. Seed yields as high as 2000 kg/hectare have been reported (National Academy of Sci- ences 1979), but yields of 300-500 kg/hectare are more typical (Ezueh 1984; Duke et al. 1977). This is comparable with typical yields from cowpea (Duke 198 l), but considerably lower than reported average yields of 1700 kg/hectare for soybean (Duke 1981). Tuber yields are typically about 1800 kg/hectare (Duke et al. 1977), compared to 2000-10 000 kg/hectare for winged bean (Duke, 1981), and 7500-18000 kg/hectare for yams in West Africa (Coursey 1967).

Sphenostylis stenocarpa is subject to attack by a number o f pests and diseases; these were listed by Okigbo (1973). Seedlings may be attacked by various insects, especially lepidopterous larvae, and foliage may be damaged by leaf-rolling cat- erpillars and leaf miners. Thrips associated with the flowers can severely damage young pods, and nematodes also attack the plants. Several fungal diseases have been observed on S. stenocarpa, including powdery mildew (Oidium sp.), leaf spot (Phoma sp.), and stem rust (Aecidium sp.). In addition, an unidentified seed-borne virus ("Af-


rican yam bean mosaic virus"; G. O. Adejare, pers. comm.) causes curling and mottling of the leaves; I have observed these symptoms on plants growing in the greenhouse. The disease suscep- tibility of this species may nonetheless be low compared to other tropical legumes (Duke et al. 1977; B. N. Okigbo, pers. comm.).

The use of S. stenocarpa, both from the wild and as a cultigen, is on the decline in tropical Africa. This is apparently the result of two factors. First, population growth is resulting in changes in the environment , reducing the avail- able habitat for wild plants; these plants are therefore now either absent or rare in many areas and knowledge of their uses is not transmitted to younger generations. Second, major crop plants, such as soybean and cowpea (for seeds) and cassava (for tubers) that have been bred for high yield, disease resistance, reduced cooking time, and other desirable traits, are replacing mi- nor crops like the African yam bean, and other minor seed (e.g., Bambara groundnut, Vigna sub- terranea (L.) Verde.) and root (e.g., Hausa potato, Solenostemon rotundifolius (Poir.) J. K. Morton) crops.

Research and breeding programs could prob- ably improve the yield and disease resistance of S. stenocarpa. The good flavor and nutritional value of the seeds and especially the tubers of S. stenocarpa, as well as its ability to grow in both dry and humid habitats, have led several authors (Okigbo 1973; Ezueh 1984; National Academy of Sciences 1979) to point out the potential value of this plant and to encourage research on its development as a food source for tropical Africa and perhaps other areas of the tropics.

In addition, S. stenocarpa represents an ideal system in which to study morphological and molecular changes that occur during the domestication of a plant. Little is known about the his- tory of this plant, which apparently represents a crop species at a relatively early stage of domestication. It is widely cultivated and locally important, but has not been subjected to extensive breeding or selection programs, and wild populations still exist over a wide geographical range. Thus, the origins of cultivated races should be easier to trace than in more widely cultivated crops where extensive human selection may have obscured relationships among taxa. In the accompanying paper, cladistic and phenetic analyses of infraspecific variation in morphometric, chloroplast DNA, and isozyme data are used to

address questions concerning the origins of ex- tant wild and domesticated races of Sphenostylis stenocarpa.

ACKNOWLEDGMENTS

I gratefully acknowledge financial assistance from the National Science Foundation (grant number BSR-8701159, to J. J. Doyle and mysel0, the Wiegand Fund of CorneU University, the Cornen University Graduate School Summer Research Travel Fund, and the Harold E. Moore, Jr. Endowment. I would also like to thank J. J. Doyle for assistance throughout the preparation of this paper; T. A. LaRue, N. F. Weeden, and J. V. Freudenstein for reviewing early drafts of the paper; F. Fawcett, M. Linkinhoker, and A. Trabka for preparing the plant illustrations; Enrique Estrada for his translation of the abstract; and D. Abbiw, A. Kitenge, T. Musasa, 1. H. Patel, and B. N. Okigbo for assistance in the field.

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Economic Botany ofSphenostylis (Leguminosae)