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Dioscorea orangeana was named by Kew botanist Paul Wilkin with colleagues from France and Madagascar, the scientific name referring to the forest in which it occurs (Forêt d'Orangea).

Dioscorea orangeana (Angona)

[KSP]

Kew Species Profiles

General Description
Dioscorea orangeana is a newly described, threatened species of edible yam from northern Madagascar.

Dioscorea orangeana was named by Kew botanist Paul Wilkin with colleagues from France and Madagascar, the scientific name referring to the forest in which it occurs (Forêt d'Orangea).

Despite a collection of this species having been made as long ago as 1960, it was only when Dr Wilkin studied this specimen in 2003, and compared it with material collected subsequently, that he discovered it was a new species of yam. This was suggested by preliminary observations that the leaf margins were often undulate (wavy), unlike most other yams in Madagascar. It was confirmed by investigating the size ranges of a number of the plant's organs.

Species Profile
Geography and distribution

Dioscorea orangeana is native to northern Madagascar. It is restricted to the Forêt d'Orangea near Diego Suarez (Antsiranana) in Antsiranana Préfecture. It occurs in deciduous forest, on sand, up to 100 metres above sea level.

Description

A twining vine to no more than 5 m, with annual stems growing from a fleshy tuber. The tuber is up to 20 cm in diameter with several digitate (finger-like) young growths below (although only one tuber has been seen by scientists). The left-twining stems are quite woody and grow to about 5 mm in diameter. They bear small brown prickles at the extreme base.

The leaves are variable in shape and colour, but often have an undulate margin, and juvenile leaves are often variegated.

Like almost all yams ( Dioscorea ), D. orangeana is dioecious - it has separate male and female plants. The male inflorescences of relatively small flowers are pendent (hang down from the vine) and are up to about 20 cm long. The male flowers are lime-green to yellow-green and in clusters of up to four. The female inflorescences are also pendent and are about 18 cm long with solitary, lime-green flowers. The flower develops into a capsule which is pale brown with chestnut-brown flecking. 

The seeds are matt dark brown and winged at the base. The wings are membranous and golden brown with slightly darker flecking.

Flowering takes place in January and February, and seeds are released from the resulting fruits in June.

Dioscorea orangeana differs from D. comorensis in having undulate leaf margins and a broader torus (the modified receptacle of the flower which bears the reproductive organs and tepals) and tepals in both the male and female flowers. In female flowers of D. orangeana the floral stipe between the ovary and the torus is shorter than in D. comorensis .

The tuber (fleshy underground stem) morphology of the species is atypical among Malagasy species in that there are several digitate lobes rather than a single tuber per growing season, although more research is needed on tuber morphology.

Threats and conservation

The conservation and sustainable use of Dioscorea orangeana are matters of concern, because its distribution is restricted to such a small area (its area of occurrence is 1.7 km²). The Forêt d'Orangea is not protected, and the nearest protected area is at least 20 km away.

D. orangeana urgently needs to be looked for in similar forests in the far north of Madagascar which is botanically poorly explored.

Uses

Dioscorea orangeana is reported to be edible. All the yams known as Angona in the Antsiranana region are favoured edible species and are heavily exploited as such.

Distribution
Madagascar
Ecology
Deciduous forest, on sand.
Conservation
Provisional IUCN Red List assessment of CR (Critically Endangered) (IUCN 2011).
Hazards

None.

[KBu]

Wilkin, P., Hladik, A., Weber, O. et al. (2009). Dioscorea orangeana (Dioscoreaceae), a new and threatened species of edible yam from northern Madagascar. Kew Bulletin 64: 461. https://doi.org/10.1007/s12225-009-9126-2

Conservation
The distribution of this species in Northern Madagascar was mapped through georeferencing the available specimens. The extent of occupancy (EOO) of Dioscorea orangeana is 3.6 km2, and its area of occurrence is 1.7 km2 using a cell size of 0.58 km2; it occupies five cells. Both of these measures suggest that the appropriate IUCN red list assessment is CR. In December 2002 CMH found a tuber on a sterile plant near Andovokonko, c. 10 km SE of Ramena, which matched the form found in Hladik 6828. Should this locality prove to hold D. orangeana, it would extend the range of the species outside the Forêt d’Orangea and increase the EOO and AOO. There is also a significant area of dry forest north of Antsiranana, in the northernmost part of Madagascar. This region is botanically poorly known, but may provide suitable habitat for D. orangeana. However, in the absence of further specimens clearly belonging to D. orangeana we suggest a provisional IUCN red list assessment of CR B1ab(iii); B2ab(iii) (IUCN 2001). Dioscorea orangeana is reported to be abundant in the Forêt d’Orangea, but the tubers are thought to be extracted in large quantities: AH and CMH saw a large number of “yam holes” in the Forêt d’Orangea. It appears that all of the yams known as Angona in the Antsiranana region are favoured edible species and thus heavily exploited. The Forêt d’Orangea is not protected, and the nearest such area is at least 20 km away.
Distribution
Found only in the Forêt d’Orangea near Antsiranana in Northern Madagascar.
Ecology
Found in deciduous forest on sand; up to 100 m.
Morphology General Habit
A twining vine to no more than 5 m, stems annual from a fleshy tuber
Morphology General Indumentum
Indumentum wholly absent, even from axillary buds
Morphology Leaves
apical leaf, more easily seen in living plants), sometimes also weakly lobed towards stem base; basal sinus 0.5 – 19 mm deep, weakly and broadly cordate to narrowly so, subhippocrepiform or with inner margins of basal lobes overlapping and sinus very narrow; apex 1.4 – 15 mm long, acuminate to long-acuminate, with a c. 0.5 – 4.5 mm long, narrowly deltoid, dark brown forerunner tip, or in broadly ovate-reniform leaves with rounded or truncate apices the acumen consists only of the forerunner tip, veins 5, only 3 reaching apex in smaller leaves with a smaller, often bifid, vein to each basal lobe, primary venation prominent on lower leaf blade surfaces; petiole 11 – 72 mm long, ± terete with longitudinal ridges and channels like stem when dry, with a broader channel on upper surface, basal and apical pulvinus drying darker, but paler green in fresh material, petiole base expanded and deltoid where it is inserted on to node, especially on lower stems, appearing homologous with cataphylls at stem base; lateral nodal organs (“stipules” of Burkill (1960)) present as a pair of fleshy, obtuse projections on either side of node; cataphylls present towards stem base, to c. 5 mm long, broadly to very broadly ovate, base clasping stem, apex acuminate, drying dark brown; bulbils (only produced in the axils of plants cultivated by Annette Hladik), pale brown, elongate-cylindrical but rather irregular, warty Leaves alternate, blade 17 – 68 × 12 – 65 mm, ovate to ovate-deltoid or ovate-sagittate, sometimes broadly ovate-orbicular, broadly ovate-reniform or orbicular-reniform, main stem leaves tending to be broader, chartaceous to thinly so, juvenile leaves often variegated by possessing an ovate to elliptic, cream to pale yellow or pale green splash with irregularly toothed margins extending from the point of petiole insertion, mid green above, paler and glossy below, drying dull olive-green, slightly paler below, sometimes with a few black glands (like those of e.g. D. trichantha Baker or D. seriflora Jum. & H. Perrier) scattered near the point of petiole insertion, glossy, circular to oval, with an annulus around the outside, less visible on upper surface where they lack an annulus and are less clearly defined; margins usually entire and undulate (e.g
Morphology Reproductive morphology Flowers
Female flowers lime-green, (sub)sessile until capsule development begins, scent not recorded; floral bract 1.2 – 1.5 × 0.5 – 1 mm, elliptic to ovate or broadly so, acuminate to long-acuminate, membranous, with a thickened midrib, bracteole like bract but shorter, narrower and inserted at 90° to it; ovary c. 4.6 – 6.6 mm long, 3-angled, oblong to narrowly elliptic-oblong in outline, green, apex acute to obtuse; floral stipe (between ovary and torus) 0.2 – 0.5 mm long; tepals spreading at anthesis, differentiated into 2 whorls of 3, thickly membranous, with a thicker midrib, inserted on the rim of a 0.5 – 0.7 × 1.3 – 1.6 mm, open, saucer- to shallowly bowl-shaped torus, texture like tepals but thickening gradually towards style bases; outer tepals 1.4 – 1.6 × 1 – 1.2 mm, ovate to broadly so, apex acute to acuminate; inner tepals 1.2 – 1.8 × 1.2 – 1.8 mm, very broadly ovate to ovate-orbicular or oblong-orbicular, apex obtuse to rounded; staminodia 6, 0.3 – 0.6 mm long, inserted around the style base near the most sharply curved part of torus, erect, filiform with a capitate, erect to recurved apex in which the upper antheriform part consists of more translucent tissue; styles 0.9 – 1.2 mm long, fused to form an erect column for c. 0.7 mm, apices free, recurved, bifid, bearing 2 deltoid, horn-like stigmas c. 0.5 mm long, spreading and borne patent to the style branch Male flowers lime-green to yellow-green, scent not recorded, pedicellate, floral bract at pedicel base 0.8 – 1.7 × 0.2 – 0.8 mm, narrowly ovate to lanceolate, acuminate, membranous, with a thicker midrib; pedicels 1 – 2.1 × 0.2 – 0.6 mm, narrowly obdeltoid in outline; tepals differentiated into 2 whorls of 3, (inner broader), membranous with a thicker midrib, both whorls inserted on a shallow, open, saucer- to bowl-shaped torus 0.3 – 1.2 × 1.3 – 2.6 mm, membranous and semi-translucent like tepals, abruptly thickened towards centre where filaments are inserted (perhaps only thickened part is true torus and the rest fused tepals); tepals erect in bud, ± patent to torus margin (i.e. spreading) at anthesis, outer whorl 1.2 – 1.9 × 1 – 1.6 mm, ovate to broadly elliptic, apex acute to acuminate, inner whorl 1.2 – 2 × 1.2 – 2.1 mm, very broadly ovate to very broadly ovate-orbicular or very broadly ovate-oblong, apex obtuse to acute; stamens inserted in a ring on a thickened area in the torus centre, filaments 0.3 – 1.2 mm long, erect at base, free and reflexed in an arching manner towards apex so that anthers face basal half of filament and are held roughly half way between torus centre and rim, anthers 0.15 – 0.45 × 0.15 – 0.35 mm, basifixed, yellow; pistillode if present concealed by anthers
Morphology Reproductive morphology Fruits
Capsule ascending at c. 45 – 5° to axis at dehiscence on a clavate, angled capsular stipe to 2.5 mm long, 19 – 29 × 10 – 12 mm, oblong to narrowly so, base shallowly retuse to rounded, apex shallowly retuse to acute, margin separating as an opercular strip, tepal bases or floral stipe usually persistent as an apiculus on each lobe of capsule, opening to more than half length to release seeds, pale brown with chestnut-brown flecking
Morphology Reproductive morphology Inflorescences
Female inflorescences to c. 18 cm long, simple, spicate, pendent, axis flattened and winged like male, colour as stem Male inflorescences 1 – 2 per axil, pendent, racemose, simple or compound through suppression of leaves in axillary shoots, where compound sterile base of primary axis c. 10 mm long, fertile part shorter, both flattened and winged like partial inflorescence axis, colour as stem; partial inflorescence bracts c. 1.5 mm long, ovate to narrowly so, acuminate, membranous, with a thicker midrib; partial inflorescence peduncle 5 – 18 mm long, axis (6.5 –) 33 – 155 × 0.5 – 1.2 mm, flattened and winged, wing widest at nodes; flowers in cymules of (1 –) 2 – 4, cymules 0.5 – 6 (– 11) mm apart, regularly to irregularly spaced, sometimes very dense towards apex where axis elongation appears to have failed or subopposite elsewhere, cymule bracts 1 per node, 1.1 – 2.1 mm long, narrowly ovate to elliptic, acuminate to long-acuminate, membranous, with a thicker midrib, cymule primary branch 0.1 – 1 mm long
Morphology Reproductive morphology Seeds
Seeds winged at base only 4.8 – 6.5 × 3.8 – 4.2 mm excluding wing, ovoid-lenticular to flattened ovoid-reniform, matt dark brown, wing 8.4 – 10.5 × 4.3 – 6.2 mm, narrowly to broadly oblong, apex obtuse to rounded, membranous, golden-brown with slightly darker flecking.
Morphology Stem
Stems left-twining, to c. 5 mm in diameter, quite woody, nodes swollen towards base above and below ground, in soil descending vertically, with a white, roughened epidermis, producing thick roots at nodes, above ground bearing small brown prickles at extreme base, grey-brown, towards base with longitudinal ridges and channels between them when dry, distal shoots terete with weak longitudinal ridges, unarmed, pale green when fresh
Note
The vernacular name Angona is also applied to Dioscorea sambiranensis R. Knuth (Burkill & Perrier 1950) amongst other species. Thus the epithet orangeana was chosen to reflect the endemic distribution of the species in the Forêt d’Orangea. Dioscorea orangeana differs from all other species of Dioscorea in Madagascar by usually possessing leaves with undulate margins. The variegated juvenile leaves may also be a useful spot character. Of the other differences between D. orangeana and D. comorensis most are discrete. In some, such as tepal width, there is a small range overlap between the two species. They are clearly different in shape, however, with D. orangeana having broader tepals in both whorls. In both species, the inner whorl of tepals is broader than the outer. It also appears that the seeds and capsules of D. orangeana are narrower than those of D. comorensis, but for both species the measurements are based on just one known fruiting specimen. Both the male and female flowers of Dioscorea orangeana have saucer- to bowl-shaped, relatively open tori like D. sterilis Weber & Wilkin and D. decaryana H. Perrier, but the torus is semi-translucent and tepal-like in texture, not thicker and opaque as in those species. The torus of D. orangeana is less deep and more open than those species with campanulate tori (Wilkin et al. 2008). In the remaining species in Madasgacar and the Comoro Archipelago, the tori are differently shaped, but they are all thicker than the tepals and opaque in dried and fresh specimens.
Phenology
Flowering in January and February, fruit developing thereafter, dehiscing in June.
Type
Madagascar. Orangea, about 1.5 km NE of Military Camp ‘Orangea’, on sandy road along trail to ocean, ♂ fl. 15 Feb. 2003, Rogers, Rakotonasolo & Vigneau 161 (holotypus P!; isotypi MO!, TAN).
Vegetative Multiplication Tubers
Tuber to c. 20 cm in diam., apically dome-shaped, with several digitate young growths below, epidermis pale to dark brown (latter in older parts), parenchyma creamy white
Vernacular
Angona (Antakarana, Sakalava, Forêt d’Orangea). However, more than one wild yam species appears to be known as Angona in the Antsiranana region.

[KSP]
Use
Dioscorea orangeana is reported to be edible.

[KBu]
Use
Tuber edible.

Native to:

Madagascar

English
Angona

Dioscorea orangeana Wilkin appears in other Kew resources:

Date Reference Identified As Barcode Type Status
Sep 3, 2014 Schatz, G.E. [4210], Madagascar K001171819
Miller, J.S. [10718], Madagascar K000523809
Randrianaivo, R. [1148], Madagascar K000523812
Miller, J.S. [10718], Madagascar K000523808
Randrianaivo, R. [1148], Madagascar K000523815
Randrianaivo, R. [1148], Madagascar K000523813
Randrianaivo, R. [1148], Madagascar K000523814

First published in Kew Bull. 64: 462 (2009)

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, 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.
  • IUCN (2001). IUCN Red List Categories: Version 3.1. Prepared by the IUCN Species Survival Commission. IUCN, Gland, Switzerland & Cambridge, UK.
  • Wilkin, P., Andrianantenaina, W. P., Jeannoda, V. & Hladik, A. (2008, publ. 2009). The species of Dioscorea L. (Dioscoreaceae) from Madagascar with campanulate tori, including a new species from Eastern Madagascar. Kew Bull. 62: 583 – 600.
  • Wilkin, P., Hladik, A., Labat, J.-N. & Barthelat, F. (2007). A new edible yam (Dioscorea L.) species endemic to Mayotte, new data on D. comorensis R. Knuth and a key to the yams of the Comoro Archipelago. Adansonia, sér. 3, 29 (2): 215 – 228.

Kew Species Profiles

  • Wilkin, P., Hladik, A., Weber, O., Hladik, C.M. & Jeannoda, V. (2009). Dioscorea orangeana (Dioscoreaceae), a new and threatened species of edible yam from northern Madagascar. Kew Bulletin 64: 461-468.

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
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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