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This species is accepted, and its native range is Madagascar.

[KBu]

Wilkin P et al. 2017. A new species of critically endangered edible yam endemic to northern Madagascar, Dioscorea irodensis (Dioscoreaceae) and its conservation. Kew Bulletin 72:15. DOI 10.1007/S12225-017-9677-6

Conservation
The specimen data cited above and field surveys to date suggest that Dioscorea irodensis occurs at no more than three localities. D. irodensis is only known to be extant at one locality south of Irodo village on the banks of the Irodo River, where it was found in 2015 and 2016 (see Map 1). It has not been possible to cross the Irodo River during field activity in 2015 and 2016 to survey the subpopulation represented by the 2002 specimen (De Block et al. 1079). In March 2016, a field team spent a day locating the coordinates of the Sahafary forest specimen (Rogers et al. 1149) and searching other suitable habitat in Sahafary forest. The specimen was collected in highly degraded vegetation on the edge of a Eucalyptus plantation. No plants of D. irodensis were seen anywhere in Sahafary. If present they would certainly have possessed above ground organs in March, thus the subpopulation has either been eradicated through habitat degradation and loss or there is an error in the GPS coordinates, perhaps caused by use of an older GPS model. For the present we must assume the former. It is likely that the subpopulation represented by De Block et al. 1079 is extant given its isolated location, so we recalculated EOO and AOO excluding only the Sahafary forest data point. This gave an EOO of less than 1 km2 and AOO of 8 km2 based on a standard cell width of 2 km. Both are below the CR threshold. In addition to habitat loss and restricted EOO/AOO, Dioscorea irodensis appears to be threatened by limited population size and extraction for use as food. At the site where it known to be extant, 10 adult plants were seen in 2015, of which 4 were female, and 15 in 2016, of which 5 were female. There is a limited reservoir of juvenile plants and a much more substantial one of seedlings with one or two leaves. A conservative estimate of generation length is 10 years; this is based on the authors’ experience of cultivating wild Dioscorea species from Madagascar from seed. Thus it could be 8 or 9 years before seeds are produced by plants that are currently juveniles or seedlings. We are in the process of acquiring data on the abundance of these life history stages via plot surveys. Approximately 80 seeds were collected for banking by the Millennium Seed Bank Partnership in March 2015. The sacred forest in which the subpopulation is found has an estimated 100 yam extraction holes, of which at least 20 appear to have been made within the last 12 months. Whilst timber extraction from the forest is culturally forbidden, removal of non-timber forest products is not. It is likely that any undiscovered subpopulations face a similar level of extraction which appears to be unsustainable. The village of Irodo has recently agreed to join the Darwin Initiative-funded project “Conserving Madagascar’s yams through cultivation for livelihoods and food security". The principal shared goal will be to conserve D. irodensis and D. maciba Jum. & H. Perrier through cultivation alongside the winged yam D. alata L. The productivity of the latter should drive down demand for wild-harvested yams. We will also collect further seed for banking and duplicate living accessions elsewhere as far as possible. In accordance with IUCN (2001) criteria, these data and observations suggest Dioscorea irodensis should be designated as CR A2acd+4acd; B1ab(i, ii, iii, iv, v)+2ab(i, ii, iii, iv, v); C1+2a(i); D (Kennerley & Wilkin, in prep.).
Ecology
Endemic to the Irodo river Valley and Sahafary forest in Antsiranana Province (Map 1) at altitudes from 30 – 230 m. It is possible that the three collections from South of the village of Irodo represent two subpopulations on either side of the river as opposed to two distinct populations (the term population is used here in an ecological sense, except in the Conservation Status section), but the specimen from Sahafary forest is spatially isolated. At Irodo, it is found in semi-deciduous forest with a canopy to 10 m and a clear shrub layer, the principal canopy trees being Colvillea and Tamarindus, with Pachypodium in the shrub layer. Soil a brown sandy loam, possibly alluvial, or red sand over limestone bedrock. The Sahafary Forest specimen states that it was from scrub forest on red sand.
Morphology General Habit
A twining vine to c. 6 m in height Capsule 23 – 28 × 15 – 19 mm, ascending at c. 75° to axis at dehiscence on recurved pedicels, obovate to oblong-obovate in outline, base rounded to truncate, apex obtuse to weakly retuse, styles persistent as a lobed apiculus, dehiscing from apex, immature capsule not seen, (sub)mature with wing thickness not exceeding 1 mm, not fleshy, pale straw-brown with red-brown markings, when mature each wing single-layered, uniformly pale to mid brown or specked with darker brown or grey-brown when dry
Morphology General Indumentum
Indumentum coarse, of colourless multicellular hairs with small inflated bases, to 1.5 mm long, erect to spreading and straight to curved, basal stems subglabrous, pubescence more extensive at nodes and on younger (narrower and angled) stems, dense on petioles and leaf blade, (lower surface less so with age), densest on buds and leaves in early stages of expansion (during male anthesis), inflorescences pubescent, most densely so on cymule bracts and tepal dorsal surfaces, especially outer whorl, capsules glabrescent but less so along axis and around style base
Morphology Leaves
Leaves borne in clusters of up to 7 on short herbaceous branches, especially on principal stems, sometimes solitary, especially on narrower stem branches and towards apices, alternate, blade (20 –) 29 – 71 × (14 –) 22 – 75 mm, ovate to very broadly so or ovate-orbicular, entire, thinly herbaceous when fresh, thin and sometimes papery when dry, sometimes translucent, drying grey to pale olive-green, paler below, paler narrowly oblong micro-organs visible at high magnification, definition and density variable, when fresh blade dark green above, paler below, veins 5 – 7, 3 reaching apex, base cordate to subtruncate, sinus depth to 8 mm, apex rounded or obtuse to acute or short-acuminate, with a forerunner tip to c. 2.5 × 1.2 mm, deltoid, green to weakly brown- pigmented when fresh, drying dark brown to concolorous with blade; petiole 10 – 54 mm long, slender, not exceeding 0.5 mm in diam in dried material, terete but longitudinally ridged, lacking a differentiated upper channel, concolorous with leaf upper surface to paler and browner, pulvinii when fresh pale green, indistinguishable when dry, central part concolorous with stem or paler
Morphology Reproductive morphology Flowers
Male flowers purple, shallowly bowl-shaped, on 0.2 – 1.1 mm long pedicels that are swollen immediately below torus, the latter 0.6 – 0.8 mm in diam., shallowly concave, opaque when dry; tepals 6, outer whorl weakly differentiated (slightly narrower), ovate to elliptic or broadly so, free, inserted on torus margin, ascending, upper half recurved at anthesis, translucent except midrib, apex rounded to acute, sometimes cucullate, outer tepals 1.1 – 1.3 × 0.5 – 0.8 mm, inner tepals 1.0 – 1.3 × 0.6 – 0.9 mm; stamens inserted on torus margin, erect, filaments 0.05 – 0.1 mm long, stout, anthers 0.25 – 0.35 × 0.25 – 0.35 mm, broadly oblong-orbicular, basifixed; pistillode 3 ridges at torus centre at 120° to each other, c. 0.2 mm in diam × 0.05 mm high
Morphology Reproductive morphology Fruits Infructescences
Infructescences 38 – 135 mm long, peduncle 8 – 30 mm long, axis colour as stems
Morphology Reproductive morphology Inflorescences
Female inflorescences unknown Inflorescences 1 per axil, spiciform, pendent; male inflorescences borne in axils of leaves that do not exceed c. 1 cm long (in early development) and appear grey-brown due to pubescence, axis to 155 mm long (including 3 – 11 mm long peduncle), slender like petiole, angled, bearing spirally arranged, irregularly spaced dense cymules of 2 – 8 flowers, rarely a solitary flower, subtended by a 1.4 – 2.1 × 0.4 – 0.6 mm, elliptic-acuminate cymule bract, each node of cymule with a 0.9 – 1.3 × 0.2 – 0.4 mm floral bract, similar to cymule bract but narrowly elliptic-acuminate to linear
Morphology Reproductive morphology Seeds
Seed winged at base only, 5.6 – 8.0 × 3.4 – 5.1 mm (excluding wing), obovate in outline, dark brown, base rounded to acute, apex obtuse to rounded, wing 5.7 – 11.2 × 5.2 – 6.7 mm, papery and translucent chestnut brown
Note
Named for the village of Irodo and the Irodo River valley where this species is found. Tuber horizontal in soil with a curved apex (derived from digging up two plants and inferring a similar position in others from the shape of extraction holes and the Malagasy vernacular name). Leaves in clusters of up to 7 on short herbaceous branches, clustered particularly towards bases of main vegetative stems (Fig. 1A, 2B), blades thin in texture, densely pubescent below and when immature but coarse and never forming a tomentum as in Dioscorea ovinala. Plants at the locality near Irodo represented by Wilkin et al. 1674 and 1675 often have white spotting on their leaf blades which has the appearance of pathogenic infection (see Fig. 2A). Male inflorescences (Fig. 1 E, F) with irregularly spaced, spirally arranged dense cymules of 2 – 8 pedicellate flowers or rarely solitary, vs flowers (sub)sessile, or rarely with a pedicel to 0.5 mm long and solitary or in groups of 2 – 4 (D. ovinala). Fruit not inflated and fleshy during development but thin-lobed and capsular throughout, single layered at dehiscence. Restricted to a small area East of Sadjoavato in Antsiranana Province. The specimen de Block et al. 1079 was included within Dioscorea sambiranensis subsp. bardotiae Wilkin by Wilkin et al. (2009) as an atypical element. Its removal to D. irodensis restricts the known distribution of D. sambiranensis subsp. bardotiae to the Montagne des Français (just one specimen) and the Réserve spéciale d’Ankarana and surrounding limestone outcrops. The resulting reduction in EOO and AOO is likely to increase the threatened status of that subspecies from Vulnerable (Wilkin et al. 2009) to Endangered and this is confirmed by recent unpublished EOO and AOO results obtained from GeoCAT.
Type
Type: Madagascar, Antsiranana: Diana, Antsiranana II, Anivorano, Irodo, ala fady S of village towards Irodo river estuary, 12°39'6.3"S 49°31'38.2"E, ♀ fr. 8 Feb. 2015, P. Wilkin, J. A. Kennerley, F. Rakotonasolo, M. Hamido & M. Tsaratiana 1675 (holotype TAN!; isotype K!).
Vegetative Multiplication Tubers
Current season’s tuber (Fig. 2C) (previous seasons’ also present) to c. 80 × 15 cm, cylindric, tapering towards base and apex, horizontal in substrate, c. 20 – 50 cm deep, epidermis pale cream, parenchyma pure white, watery, not mucilaginous, apex curved 90° and narrowing to c. 3 mm, subtended by a c. 8 mm diam., thickened crown; stem above crown erect, annual, below ground white, above ground to 3 mm in diam., terete, unarmed, tough and wiry, dark purple with green flecks to brown and mottled paler, drying dark brown on principal stems, paler on branches, possessing cataphylls towards stem base to c. 4 × 3 mm, very broadly ovate, apex acute to short-acuminate, amplexicaul, thick and leathery; axillary bulbils not present; nodes on main stems and towards base especially swollen to c. 6 mm, often with a pair of rigid, aculeate lateral projections, occasionally more projections present
Vernacular
Bemandry in the village of Irodo. This name appears to be applied particularly to species with horizontal tubers, for example the element of Dioscorea soso Jum. & H. Perrier sensu lato with the same tuber habit.

[KBu]
Use
Tuber edible cooked. Rather watery following cooking and thus not fully satisfying the appetite. Dioscorea maciba, known as batatala in Irodo, is the more sought after species of the two that are found in the Irodo valley and surrounding areas. Not believed to be sold in markets but consumed usually in March/April.

Native to:

Madagascar

Dioscorea irodensis Wilkin, Rajaonah & Randriamb. appears in other Kew resources:

First published in Kew Bull. 72(1)-15: 2 (2017)

Accepted by

  • Govaerts, R., Nic Lughadha, E., Black, N., Turner, R. & Paton, A. (2021). The World Checklist of Vascular Plants, a continuously updated resource for exploring global plant diversity. https://doi.org/10.1038/s41597-021-00997-6 Scientific Data 8: 215.

Literature

Kew Bulletin

  • Bachman, S., Moat, J., Hill, A. W., de la Torre, J. & Scott, B. (2011). Supporting Red List threat assessments with GeoCAT: geospatial conservation assessment tool. In: V. Smith & L. Penev (eds), e-Infrastructures for data publishing in biodiversity science. Zookeys 150: 117 – 126 (Version BETA).
  • IUCN (2001). Red List Categories and Criteria: Version 3.1. http://www.iucnredlist.org/static/categories_criteria_3_1 [accessed 2016-04-07].
  • IUCN Standards and Petitions Subcommittee (2014). Guidelines for using the IUCN Red List Categories and Criteria. Version 11. Prepared by the Standards and Petitions Subcommittee. Downloadable from http://www.iucnredlist.org/documents/RedListGuidelines.pdf [accessed 2016-04-07].
  • Kennerley, J. A. & Wilkin, P. (in prep.) Dioscorea irodensis. The IUCN Red List of Threatened Species.
  • Shorthouse D. P. (2010). SimpleMappr, an online tool to produce publication-quality point maps. http://www.simplemappr.net [accessed 2016-04-07]
  • Thiers, B. (2012). Index Herbariorum, a global directory of public herbaria and associated staff. New York Botanical Garden’s virtual herbarium. Available from: http://sweetgum.nybg.org/ih/ [accessed 2016-04-07].
  • Viruel, J., Segarra-Moragues, J., Raz, L., Forest, F., Wilkin, P., Sanmartín, I. & Catalán, P. (2016). Late Cretaceous–Early Eocene origin of yams (Dioscorea, Dioscoreaceae) in the Laurasian Palaearctic and their subsequent Oligocene–Miocene diversification. J. Biogeogr. 43: 750 – 762.CrossRefGoogle Scholar
  • Wilkin, P. & Randriamboavonjy, T. (2012). Nomenclatural changes in yams of Madagascar (Dioscorea: Dioscoreaceae). Kew Bull. 67: 63 – 67.
  • Wilkin, P., Hladik, A., Jeannoda, V. & Weber, O. (2009). The threatened edible yams of the Dioscorea sambiranensis R. Knuth species complex: a new species and subspecies. Adansonia 31: 249 – 266.
  • 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.CrossRefGoogle Scholar

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