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Despite having large tubers weighing up to 5.5 kg, distinctive vegetative and floral morphology and being an especially sought-after food plant, the yam species known as 'bako' in the Sakalava language has only just been formally described by botanists.

Dioscorea bako (bako)

[KSP]

Kew Species Profiles

General Description

Despite having large tubers weighing up to 5.5 kg, distinctive vegetative and floral morphology and being an especially sought-after food plant, the yam species known as 'bako' in the Sakalava language has only just been formally described by botanists.

It was collated by Mamy Tiana Rajaonah, Vololoniaina Jeannoda and Kew's Paul Wilkin during work on the 'Yams of Madagascar' project, a collaborative research programme of the Département de Biologie et Ecologie Végétales, Université d'Antananarivo and Kew.

Its exploitation as a favoured starch source, coupled with its restricted distribution, place it under significant threat of extinction. Research is underway on the conservation of bako, ensuring that future use is sustainable, but the work needs more resources.

Species Profile
Geography and distribution

Dioscorea bako is restricted to deciduous forests near Morondava in western Madagascar.

Description

Dioscorea bako is a stem-twining herbaceous vine with male and female flowers on separate plants (like most Dioscorea species) to 5 m in height. Its tubers can attain 1.5 m in length and 5.5 kg in weight.

Above ground, its leaf lower surface is greyish-green and the leaf margins usually shallowly and irregularly lobed. Its male inflorescences are borne on short specialised leafless shoots towards the stem base, and possess dense, overlapping hairy bracts for most of their length, giving a catkin-like appearance. The small and inconspicuous flowers are found between the bracts. 

Female flowering plants have not yet been seen, but the capsular fruits are 3-winged and obovate (egg-shaped with the narrow end at the base) to narrowly obovate-oblong in outline, and contain basally winged seeds like most of the species' close relatives in Madagascar.

Threats and conservation

The conservation status of Dioscorea bako has been assessed as Endangered based on IUCN (International Union for Conservation of Nature) criteria.

Bako is a favoured starch source in the area around Morondava in western Madagascar where it occurs. The people of the region report that it is becoming harder to find, probably because it has been over-extracted. It is also threatened by habitat loss.

Efforts to conserve this species have begun, but the level of threat to this species is high. Like many of the edible wild yams of Madagascar, a biodiversity hotspot, it is found in just a small area of this large continental island but is of great local value and importance as a source of food.

At least 12 of the other 30 (approximately) edible yam species in Madagascar are threatened, highlighting the need for a country-wide yam conservation programme as a step towards food security. 

Uses

The tuber is a source of starch; the constituents are cut into pieces, boiled, and eaten as a main meal or snack.

Cultivation

Dioscorea bako is known only from the wild, but cultivation experiments have been attempted in the last few years as a means of conservation.

Distribution
Madagascar
Ecology
Deciduous forest.
Conservation
IUCN status of Endangered (EN).
Hazards

None.

[KBu]

Wilkin, P., Rajaonah, M.T., Jeannoda, V.H. et al. 2008. An endangered new species of edible yam (Dioscorea, Dioscoreaceae) from Western Madagascar and its conservation. Kew Bulletin 63: 113. DOI: https://doi.org/10.1007/s12225-007-9000-z

Conservation
IUCN Red List category EN B2b(iii)(iv)C (IUCN 2001). The four localities of the five specimens cited above give an extent of occurrence (EOO) of 137.5 km2. At a cell size of 3.116 km2 (see Willis et al.2003 for a discussion of the importance of cell size), Dioscoreabako occupies four cells with an area of occupancy (AOO) of 38.84 km2 and has four sub-populations based on grid adjacency. If a cell size of 10 km2 is used (the software can overestimate cell size near coastlines), D. bako has an AOO of 300 km2 with two subpopulations based on grid adjacency. All of the above measures indicate that it is Endangered. Rapoport Analysis (Rapoport 1982) gives an AOO of 1,010.03 km2 and two subpopulations. The discovery of the species in July 2006 in the commune of Ampanihy will increase the EOO and AOO of the species, but is unlikely to do so sufficiently to place it in a different IUCN Red List category.
Distribution
Endemic to Morondava Préfecture in Western Madagascar, currently known from Réserve Spéciale d’Andranomena, Kirindy Forest and the surrounding area. Dioscorea alatipes is also a narrow endemic found only near Toliara on limestone or sandy soils. In July 2006, while this paper was being drafted, further individuals of D. bako were encountered by V. Jeannoda, but not collected, in the southern part of Menabe, in the commune of Ampanihy, south of the Kabatomena river and the town of Mahabo.
Ecology
Deciduous forest on sandy, loamy, lateritic or stony soils, sometimes in partially disturbed areas or light gaps but also encountered in deep shade and in wetter habitats. Altitude c. 20 m. Flowering from December to February, capsules dehiscing in June or July. In research on the yams of the Morondava region (as part of a paper on the diversity, cultural role, management and nutritional value of the yams of Madagascar [Jeannodaet al., pers. comm.]), Dioscoreabako was shown to be one of 10 species encountered there. This species was found infrequently at Andranomena in partially logged deciduous forest on very sandy loam soils, and in much greater abundance at Beroboka in a cultivated area on sandy clay soil near water. The recently discovered population(s) at Ampanihy showed the same ecological preferences.
Morphology General Habit
A twining vine to at least 5 m, stems annual from a fleshy tuber
Morphology General Indumentum
Indumentum consisting of unicellular, straight to crisped simple hairs to 0.6 mm long, sparingly present on stems, more dense around nodes and on young vegetative growth, dense on peduncles and very dense on short specialised shoots bearing inflorescences and partial inflorescence bracts so that the latter appear grey-brown when dry
Morphology Leaves
Leaves alternate; blade 2.6 – 7.4 × 2.6 – 7.7 cm, shape variable, ovate or ovate-oblong to broadly so, rarely broadly reniform, chartaceous, mid- to dark matt green above, paler and greyish-green below, drying grey- or olive-brown, margins rarely entire, usually shallowly and irregularly lobed, base broadly cuneate at point of petiole insertion onto blade where main veins diverge, but overall shape shallowly to deeply cordate, sinus to 1.7 cm deep, apex acute or acuminate with a 2 – 5 mm long deltoid forerunner tip, concolorous with blade or slightly paler, veins 5, with a smaller, often bifid, vein to each basal lobe, sunk in depressions in blade in fresh material; petiole 2.6 – 5.2 cm long, terete but channelled on upper surface, shiny pale green, basal and apical pulvini slightly darker in herbarium specimens; lateral nodal flanges (‘stipules’ of Burkill1960) present as an expansion of the petiole at its point of insertion onto the stem node and two reflexed fleshy projections on either side of the node
Morphology Reproductive morphology Flowers
Female flowers unknown Fertile male flowers yellow, scent not recorded, on pedicels 0.6 – 1.5 mm long, longitudinally ridged and slightly thickened towards apex; tepals 6, in two whorls, ±free, ascending, margins membranous, central area thickened and reticulate in appearance, with a fine midrib, tepals inserted on a flat, thin discoid torus c. 0.8 mm in diam., outer whorl 1.1 – 1.4 × 0.5 – 0.8 mm, elliptic or ovate to narrowly so, apex acute, inner whorl 0.9 – 1.1 × 0.5 – 0.8(– 0.9) mm, elliptic to elliptic-oblong, apex obtuse, stamens erect, filaments very short, to 0.2 mm long , anthers 0.2 – 0.4 × 0.2 – 0.4 mm, oblong-orbicular, basifixed; pistillode absent Sterile flowers with a c. 1.4 × 0.9 mm, swollen, obovoid receptacle possessing several raised longitudinal ridges; tepals 1.5 – 2.7 mm long, thickened and opaque in dried material, narrowly elliptic, lanceolate or narrowly elliptic-oblong, erect, apices sometimes extended, membranous and with similar pubescence to cymule bracts, especially in outer whorl, or rounded to obtuse, weakly developed staminodia and pistillodia sometimes present inside flower
Morphology Reproductive morphology Fruits
Capsules reflexed at maturity at c. 30 – 45° to axis, (17 –)19 – 22  × (9.5 –)11 – 13 mm, narrowly obovate to narrowly obovate-oblong in outline, pale tan with many small dark to very dark brown markings, especially on axis and towards margin, base rounded to broadly cuneate, apex rounded to acute with a projection (floral remains) on each valve; capsular stipes 1.6 – 2.5 mm long, obdeltoid, three-angled, reflexed
Morphology Reproductive morphology Inflorescences
Male inflorescences up to 12 per axil, on short specialised leafless shoots (to 2.5 cm long) in the axils of cataphylls towards stem base, two to three simple inflorescences per leaf axil above; partial/simple inflorescences with primary axis 1.5 – 9.5 cm long, peduncle (sterile basal region of partial inflorescence) 0.4 – 2.5 cm long, racemose, pendent, a few basal bracts relatively laxly distributed, but bracts dense and overlapping for most of the axis length and giving a catkin-like appearance; cymule bracts 2.3 – 3 × 1.8 – 2.4 mm, borne on a ridged inflorescence axis concealed by bracts and flowers, sessile, broadly ovate to orbicular, thinly chartaceous with a single thickened midrib, apex strongly acuminate; each bract concealing a bracteole orientated at 90° to the bract, bracteole 2 – 2.8 mm long, narrowly ovate to elliptic, membranous, with a thicker midrib, apex acuminate; bracteole subtending a sessile sterile flower, sessile sterile flower subtending in turn a cymule of (2 –)3(– 5) male flowers which are exserted from the bract, cymule primary branch 0.2 – 1.3 mm long, longitudinally ridged or flattened, floral bracts at each node of the cymule 0.7 – 1.2 mm long, smaller towards cymule apex, ovate to lanceolate, glabrous, membranous, sometimes with a fine midrib Female infructescences one per axil, simple, spicate, pendent; peduncle 38 – 53 mm long, narrower than axis but thickening towards apex, flattened and two-winged; axis 60 – 90 × 0.9 – 1.8 mm, ridged and angled, capsules solitary, c. 2 – 10 mm apart, denser towards apex where capsules overlap for much of their length, ovaries often aborted towards base
Morphology Reproductive morphology Seeds
Seeds winged at base only, 4.6 – 5.5 × 3.2 – 4 mm, flattened ovoid-lenticular to subreniform-lenticular, matt brown, wing (8.3 –)10 – 12.5 × 4.8 – 6 mm (upper seed of two in each locule has shorter wing), oblong to narrowly ovate, apex obtuse to rounded, golden-brown, translucent
Morphology Stem
Stems left-twining, to at least 8 mm in diameter in flowering individuals, terete, unarmed but roughened by means of russet-brown processes, and also black processes on older stems, white below ground, greyish-white towards base above it, green with greyish flecking above; cataphylls present towards stem base, to c. 1.5 cm long, narrowly ovate to elliptic or lanceolate, brownish-grey, chartaceous, apex acute to acuminate; bulbils not present
Note
The type specimen has no leaves. This is unfortunate, but it is the only currently available specimen that has flowers at anthesis. The Sakalava name Bako was selected as the specific epithet for this species in order to preserve the Malagasy name of this plant and to continue the tradition established by Perrier of formalising vernacular names for Malagasy taxa of Dioscoreaceae. It can be recognised in the field by its leaf blades, which have shallowly and irregularly lobed margins, are grey-green below, and are broadly cuneate at the point of petiole insertion, and by its male inflorescences, which are borne towards the stem base with dense, overlapping, pubescent bracts.
Type
Madagascar, Toliara Province, Morondava Préfecture, Mahabo Subpréfecture, Réserve Spéciale d’Andranomena, ♂, fl. Dec. 2002, Rajaonah MT 006 (holotypus DBEV; isotypus K!).
Vegetative Multiplication Tubers
Tubers annually replaced, those of current rainy season and previous rainy season present (e.g., Wilkin et al-1137 and 1145), divergent, to c. 150  ×  20 cm and 5.5 kg in weight when dug for food (Jeannodaet al-2003; Rajaonah2004), cylindric to fusiform or narrowly claviform, epidermis pale brown, parenchyma pure white, mucilaginous, crown white or pink, thickened, appearing to lack scales, c. 30 – 40 cm below the soil surface
Vernacular
Bako (Sakalava).

[KSP]
Use
Starch source.

[KBu]
Use
The tuber of Dioscorea bako is edible and, with D. maciba Jum. & H. Perr., is the favoured yam of people of the Morondava region (Jeannodaet al.2003, 2007; Rajaonah2004). The tubers, which reach maturity in April, are peeled, washed, and cut into c. 12 – 20 or 2 – 4 cm long pieces. These are boiled in water deep enough to cover them and served with either fish or honey as a main meal or alone as a snack. The larger pieces are called sambaiky in Sakalava when cooked, whereas the smaller, which have a softer consistency, are called katokato (Rajaonah2004).

Native to:

Madagascar

English
Bako

Dioscorea bako Wilkin appears in other Kew resources:

Date Reference Identified As Barcode Type Status
Wilkin, P. [1145], Madagascar K000523600
Hanitrarivo, R.M. [HRM 039], Madagascar K001171769
Hanitrarivo, R.M. [HRM 166], Madagascar K001171770
Wilkin, P. [1145], Madagascar K000523599
Wilkin, P. [1145], Madagascar K000523602
Tahinarivony, A.J. [TAJ 592], Madagascar K001171768
Wilkin, P. [1137], Madagascar K000523598
Wilkin, P. [1137], Madagascar K000523597
Wilkin, P. [1145], Madagascar K000523601
Wilkin, P. [1137], Madagascar K000523596

First published in Kew Bull. 63: 114 (2008)

Accepted by

  • Govaerts, R.H.A. (2011). World checklist of selected plant families published update Facilitated by the Trustees of the Royal Botanic Gardens, Kew.

Literature

Kew Bulletin

  • Burkill, I. H. & Perrier de la Bâthie, H. (1950). Dioscoréacées. In: H. Humbert (ed.), Flore de Madagascar et des Comores. Muséum National d’Histoire Naturelle, Paris.
  • Burkill, I. H. (1960). The organography and the evolution of the Dioscoreaceae, the family of the yams. J. Linn. Soc., Bot. 56: 319 – 412.
  • Haigh, A., Wilkin, P. & Rakotonasolo, F. (2005). A new species of Dioscorea L. (Dioscoreaceae) from western Madagascar and its distribution and conservation status. Kew Bull. 60: 273 – 281.
  • IUCN (2001). IUCN Red List Categories: Version 3.1. IUCN Species Survivial Commission, Gland, Switzerland.
  • Jeannoda, V., Jeannoda, V. H., Hladik, A. & Hladik, C. M. (2003). Les ignames de Madagascar; diversité, utilisations et perceptions. Hommes et Plantes 47: 10 – 23.
  • Jeannoda, V., Razanamparany, J., Rajaonah, M. T., Monneuse, M. O., Hladik, A. & Hladik, C. M. (2007). Les ignames (Dioscorea spp.) de Madagascar: espèces endémiques et formes introduites; diversité, perception, valeurnutritionnelle et systèmes de gestion. Rev. Ecol. (Terre et Vie) 62: 191 – 207.
  • Rajaonah, M. T. M. (2004). Études Biologique, Anatomique, Ecologique et Ethnobotanique des espèces de Dioscorea (Dioscoreaceae) dans la region du Menabe. Unpublished DEA thesis, Département de Biologie et Ecologie Végétales, Faculté des Sciences, Université d’Antananarivo.
  • Rapoport, E. H. (1982). Areography: Geographical Strategies of Species. Pergamon Press, New York.
  • Schols, P., Furness, C. A., Wilkin, P., Smets, E., Cielen, V. & Huysmans, S. (2003). Pollen morphology of Dioscorea (Dioscoreaceae) and its relation to systematics. Bot. J. Linn. Soc. 143: 375 – 390.
  • Schols, P., Wilkin, P., Furness, C. A., Huysmans S. & Smets, E. (2005). Pollen evolution in yams (Dioscorea, Dioscoreaceae). Syst. Bot. 30: 750 – 758.
  • Weber, O., Wilkin, P. & Rakotonasolo, F. (2005). A new species of edible yam (Dioscorea L.) from western Madagascar. Kew Bull. 60: 283 – 291.
  • Weberling, F. (1989). Morphology of Flowers and Inflorescences. Cambridge University Press, Cambridge.
  • Wilkin, P., Rakotonasolo, F., Schols, P., & Furness, C. A. (2002). A new species of Dioscorea (Dioscoreaceae) from Western Madagascar and its pollen morphology. Kew Bull. 57: 901 – 909.
  • Wilkin, P., Schols, P., Chase, M. W., Chayamarit, K., Furness, C. A., Huysmans, S., Rakotonasolo, F., Smets, E. & Thapyai, C. (2005). A plastid gene phylogeny of the yam genus, Dioscorea: roots, fruits and Madagascar. Syst. Bot. 30: 736 – 749.
  • Willis, F., Moat, J. & Paton, A. (2003). Defining a role for herbarium data in Red List assessments: a case study of Plectranthus from eastern and southern Africa. Biodivers. Conserv. 12: 1537 – 1552.

Kew Species Profiles

  • Wilkin, P., Rajaonah, M.T., Jeannoda, V.H., Hladik, A, Jeannoda, V.L. & Hladik C.M. (2008). An endangered new species of edible yam ( Dioscorea, Dioscoreaceae) from Western Madagascar and its conservation. Kew Bulletin. 63: 113-120.

Herbarium Catalogue Specimens
Digital Image © Board of Trustees, RBG Kew http://creativecommons.org/licenses/by/3.0/

Kew Backbone Distributions
The International Plant Names Index and World Checklist of Selected Plant Families 2021. Published on the Internet at http://www.ipni.org and http://apps.kew.org/wcsp/
© Copyright 2017 World Checklist of Selected Plant Families. http://creativecommons.org/licenses/by/3.0

Kew Bulletin
Kew Bulletin
http://creativecommons.org/licenses/by-nc-sa/3.0

Kew Names and Taxonomic Backbone
The International Plant Names Index and World Checklist of Selected Plant Families 2021. Published on the Internet at http://www.ipni.org and http://apps.kew.org/wcsp/
© Copyright 2017 International Plant Names Index and World Checklist of Selected Plant Families. http://creativecommons.org/licenses/by/3.0

Kew Species Profiles
Kew Species Profiles
http://creativecommons.org/licenses/by-nc-sa/3.0