Gastrodia elatoides W.C.Huang, G.W.Hu & Q.F.Wang, 2018

Huang, Wei-Chang, Wang, Zhen-Wei, Wei, Neng, Zhu, Jiao, Lan, Si-Ren, Hu, Guang-Wan & Wang, Qing-Feng, 2018, Gastrodia elatoides (Orchidaceae: Epidendroideae: Gastrodieae), a new holomycoheterotrophic orchid from Madagascar, Phytotaxa 349 (2), pp. 167-172 : 167-171

Gastrodia elatoides W.C.Huang, G.W.Hu & Q.F.Wang sp. nov. ( Figs. 1 & 2 )

Type:— MADAGASCAR. Antsiranana: Montagne D’Ambre National Park, under rainforest, 12°31 ′ 13 ″ S, 49°10 ′ 23 ″ E, 1050 m 15 Sept. 2017, Huang, Wang & Hu CSH-2017034 (holotype: CSH).

The new species resembles G. elata but differs in its bracts being triangular-ovate to triangular-lanceolate, obviously trinerved, with the base surrounding the pedicel, lip having an entire apical margin, a trilobed epichile, a pruinose hypochile with a longitudinal keel and the ovary being verrucose.

Terrestrial, holomycotrophic herbs, ca. 70 cm tall. Rhizome tuberous, obconical-ellipsoid, ca. 9 cm long, 1.8 cm in diam., slightly flattened, nodes closely spaced with triangular scales, the upper part densely covered with lanate hairs. Raceme erect, peduncle ca. 60 cm tall, glabrous, brown to whitish, with 10 membranous sheaths; sheaths tubular, 8–10 mm long. Inflorescence with 32 flowers, rachis ca. 10 cm long; bracts triangular-ovate to triangular-lanceolate, 6–7 × 2–4 mm, nearly equal the length of pedicel plus ovary, dark greyish brown to dark brown, membranous, obviously trinerved, base surrounding the pedicel, apex acute. Pedicel white, ca. 3 mm long. Flower only opening slightly, resupinate, suberect; perianth tube urceolate with 4 ridges, base dilated towards the front, 8–9 × 5–7 mm, outer surface subglabrous, yellowish green, inside surface greyish green to light green; sepal lobes 3, broadly triangular-ovate, subequal, ca. 3 mm long, light green except yellowish green at apex, apex obtuse; petal lobes 2, broadly ovate to nearly round, base contracted, smaller than sepal lobes, ca. 2 mm long, yellowish green. Lip 6–7 × 3 mm, attached to the column foot, enclosed within perianth tube except for the apex; epichile trilobed, 4.0–4.5 × 3.0 mm, yellowish white, 2 lateral lobes erect, midlobe slightly decurved and yellow at apex, margin entire, apical half sparsely irregularly crisped; hypochile contracted into a claw, ca. 3 × 2 mm, middle part fused to the perianth tube, with a longitudinal keel in the middle, looking like an extension of the column foot, bilateral parts free, front half with a pair of gibbous folds, abaxial surface smooth, bluish green, adaxial surface bluish white, pruinose. Column straight, 7–8 mm long, with a tooth-like stelidium on each lateral side of the apex, stigmatic surface located at basal part with nectary, column foot short, ca. 1mm, fused on the perianth tube; rostellum well developed, 0.7 × 1.5 mm, anther hemispherical, ca. 1.5 mm in diam.; pollinia 2, granular, composed of friable massulae, without caudicles. Ovary obconical, ca. 3 mm long, verrucose, yellowish brown to dark brown. Fruits and seeds not seen.

Phenology:— Flowering in September.

Etymology:— Referring to the similarity of this species to G. elata .

Distribution and ecology:— The new species has only been found in North Madagascar in one rare population under rainforest trees in Montagne D’Ambre National Park. Gastrodia species are intricately linked to their habitat, owing to their specific mycorrhizal associations throughout their life cycle ( Martos et al. 2009, Selosse et al. 2010, Martos et al. 2015). It is possible that G. elatoides occurs in adjacent areas that have not yet been fully explored.

Conservation status:— This new species was only found at Montagne D’Ambre National Park. Since there is not enough data on population size, an assessment of the current conservation status of this species cannot be produced until further investigations have been conducted. Therefore, we suggest evaluating this species as data deficient (DD) according to the IUCN Red List Categories and Criteria ( IUCN 2001).

Taxonomic notes:— Because the plant reaches 70 cm in height during flowering and possesses an urceolate perianth tube, Gastrodia elatoides should be included in G. section Gastrodia . It shows great similarity to G. elata in its triangular scales on a densely noded rhizome, height of peduncle, suberect and weakly opening flower, urceolate perianth tube with its base dilated towards the front and column elongate with the stigmatic surface located at basal part with the nectary and two tooth-like apical stelidia. However, the differences between them are also clear, including its triangular-ovate to triangular-lanceolate obviously trinerved bracts with the base surrounding the pedicel (vs. bracts oblong-lanceolate, veins not obvious and base not surrounding the pedicel in G. elata ), apical margin of lip entire (vs. apical margin irregularly fimbriate in G. elata ), epichile strongly trilobed (vs. epichile obscurely trilobed in G. elata ), hypochile pruinose (vs. hypochile glabrous in G. elata ) and ovary surface verrucose (vs. ovary surface smooth in G. elata ). More detailed comparisons between G. elatoides and G. elata are presented in Table 1.

In tropical Afro-Madagascar, five species of Gastrodia have been reported, all of scattered distribution and rare occurrence ( Cribb et al. 2010, Martos et al. 2015), namely G. africana Kraenzlin (1900: 179) , G. rwandensis Fischer & Killmann (2010: 317) , G. ballii Cribb & Browning (2010: 317) , G. madagascariensis Perrier ex Martos & Bytebier (2015: 49) and G. similis Bosser (2006: 52) . Based on their characteristics such as campanulate perianth tube, inflorescence only 3–15 cm long during flowering ( Schlechter 1911, Chung & Hsu 2006), all five of these species belong to G. section Codonanthus Schlechter (1911: 409) . In contrast, this newly discovered species has an inflorescence reaching to 70 cm long during flowering and an urceolate perianth tube, making it a member of G. section Gastrodia .

Biogeographical study would be helpful to understand the evolutionary history of this unusual species. Martos et al. (2015) indicated that nuclear and mitochondrial markers would be suitable to resolve phylogenetic relationships within Gastrodia . Since Schlechter’s taxonomic treatment of Gastrodia over one century ago included less than 20 species, an updated and comprehensive classification is now needed.

Figures

FIGURE 1. Gastrodia elatoides. A. Inflorescence. B. Tuber and lower part of peduncle with membranous sheaths. C. Dorsal view of flower. D. Front view of flower. E. Column, lip and ovary. F. Lip. G. Column. H. Pollinia. I. Top view anther cap. J. Bottom view of anther cap. Drawn by Tian Jing.

FIGURE 2. Gastrodia elatoides. A. Habitat. B. The whole plant. C. Inflorescence. D. Tuber and peduncle with tubular sheaths. E. Front view of flower. F. Lateral view of flower. G. Dorsal view of flower. H. Bract. I. Column. J. Upper part of column without anther, showing the rostellum. K–L. Pollinia and anther cap (K, bottom view; L, top view). M–N. Dissected flower showing the lip. Scale bars:A = 20 cm; C, D = 2 cm; E, F, G, H, I = 5 mm; J, K, L, M, N = 2 mm.