1. Family: Dioscoreaceae R.Br.
    1. Genus: Dioscorea Plum. ex L.
      1. Dioscorea orangeana Wilkin

        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).

    [KSP]
    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 orangeanais 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.

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

    Images

    Distribution

    Found In:

    Madagascar

    Common Names

    English
    Angona

    Dioscorea orangeana Wilkin appears in other Kew resources:

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

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

    Accepted in:

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

    Literature

    • [2] 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.

    Sources

    International Plant Names Index
    The International Plant Names Index (2016). Published on the Internet http://www.ipni.org
    [A] © Copyright 2016 International Plant Names Index. https://creativecommons.org/licenses/by/3.0

    Kew Species Profiles
    Kew Species Profiles
    [B] http://creativecommons.org/licenses/by-nc-sa/3.0
    [C]

    World Checklist of Selected Plant Families
    World Checklist of Selected Plant Families(2016). Published on the Internet http://apps.kew.org/wcsp/
    [D] See http://kew.org/about-kew/website-information/legal-notices/index.htm You may use data on these Terms and Conditions and on further condition that: The data is not used for commercial purposes; You may copy and retain data solely for scholarly, educational or research purposes; You may not publish our data, except for small extracts provided for illustrative purposes and duly acknowledged; You acknowledge the source of the data by the words "With the permission of the Trustees of the Royal Botanic Gardens, Kew" in a position which is reasonably prominent in view of your use of the data; Any other use of data or any other content from this website may only be made with our prior written agreement. http://creativecommons.org/licenses/by-nc-sa/3.0
    [E] © Copyright 2016 International Plant Names Index and World Checkist of Selected Plant Families. https://creativecommons.org/licenses/by/3.0