Gastrodia thilakapremae Atthanagoda, C.Bandara & Kumar, 2023

Bandara, Champika, Atthanagoda, Anusha Gayan, Bandara, Nadeesha Lewke & Kumar, Pankaj, 2023, The study of the tribe Gastrodieae (Orchidaceae, Epidendroideae) in Sri Lanka I: two new species of Gastrodia, Phytotaxa 622 (2), pp. 115-130 : 121-126

publication ID	https://doi.org/ 10.11646/phytotaxa.622.2.2
DOI	https://doi.org/10.5281/zenodo.10164588
persistent identifier	https://treatment.plazi.org/id/03B1553F-4A0C-DD03-5ECC-1D85FBDCFCFE
treatment provided by	Plazi
scientific name	Gastrodia thilakapremae Atthanagoda, C.Bandara & Kumar
status	sp. nov.

Treatment

Gastrodia thilakapremae Atthanagoda, C.Bandara & Kumar View in CoL sp. nov. ( Figs. 1 F–K View FIGURE 1 , 4 View FIGURE 4 & 5 View FIGURE 5 )

Type:— SRI LANKA. Central Province, Kandy District, Kondagala in Loolkandura Estate , 26 May 2022, AKAG12.2022 (holotype PDA!; isotype PDA!-spirit) ; Sabaragamuwa Province, Ratnapura District, Galwangediya, Eratne –Sri Pada trail, Samanala Nature Reserve , 10 June 2022, AKAG13.2022 (paratype PDA!; PDA!-spirit) .

Diagnosis: Gastrodia thilakapremae , a Sri Lankan endemic, is not easy to differentiate from a Japan and Taiwan native G. gracilis Blume (1856: 174) as they look similar in various morphological features, however they are different on a closer look. Gastrodia thilakapremae has green flowers with green opaque petals; triangular floral bracts, 4.5–6 mm long; orange labellum (darker towards apex and fading towards base), length slightly shorter than column with anther cap, almost triangular to ovate in shape abruptly narrowing towards the apex with constrictions on the margins, lacking distinct longitudinal bands of intermittent warts towards the centre, with a pair of triangular lamellae on the centre between the constrictions; hypochile broad (> 2 mm wide) and orange on upper and white on the lower surface; epichile lower margin slightly flat; column with stelidia wings broadening from nearly at the base of the column till just below the apex of stelidia and capsules fusiform, 2.5–3.5 cm long. Whereas, G. gracilis has dull greenish-brown flowers with darker pale brown petals; floral bracts ovate or elliptic shaped, 2–4 mm long; labellum orange with white longitudinal bands before the margin on either side, length slightly longer than the column with anther cap, almost triangular but gradually narrowing towards apex lacking any constrictions on the margin; distinct 5 longitudinal divergent bands of intermittent warts running from base to the middle of the labellum, with a pair of ellipsoid lamellae towards the apex; hypochile narrow (<2 mm wide) and orange on both surfaces; lower margin of epichile raised up to fill the gap caused due to lack of wings on lower margin of the column; column with broadening of stelidia wings not starting from base but after 1/3 rd of the length from base and obovoid or ellipsoid capsules that are 2–2.3 cm long (see Fig. 6 View FIGURE 6 ).

Terrestrial, holomycoheterotrophic herbs, 55–75 cm tall. Rhizome tuberous, ellipsoid, 4–6 cm long, 1.0– 1.3 cm in diameter, sparse hairs dispersed along the gaps between closely placed membranous triangular scales emerging from the nodes. Raceme erect, peduncle 40–46 cm long, glabrous, pale brown or greyish-brown, with 8–10 membranous semi-transparent sheaths; sheaths tubular, pale brown, 5.5–7 mm long. Inflorescence erect with 4–6 flowers, rachis ca. 4–6 cm long. Floral bracts triangular, 4.5–6 mm, acute, dark brown, base surrounding the pedicel. Pedicel dull green-brown to dark brown, verrucose, ca. 4–6 mm long. Flowers resupinate, perianth tube formed by fusion of sepals and petals, apical end partially opened; perianth tube slightly arched downwards, nodding, 2.2–2.5 cm long, up to 1.6–1.8 cm wide, globose, outer surface dull green, verruculose; inner surface pale green; lobe of dorsal sepal broadly ovate, 9–10 × 6 mm, apex obtuse, slightly convex, fleshy, yellowish-green to pale green, margins entire; lobes of lateral sepals broadly ovate, 8–9 × 4.5–5.5 mm, obtuse, fleshy, margins entire, yellow-green on outside, pale green inside; petal lobes 2, orbicular with contracted base, curled, smaller than sepal lobes, 5.5 × 5 mm, obtuse, margin crenate, pale green; labellum adnate to column foot, ovate to rhomboid, 5.5–6.3 mm long, 2.3–4.5 mm wide, enclosed within the perianth tube, orange, longitudinally channeled underneath; epichile abruptly narrowing at the apex, 5.2–5.4 mm long, 3.5–4.5 mm wide, dark orange, apex yellow, irregularly crisped on the margin; hypochile contracted into a claw, ca. 0.6–0.8 mm long, 2.1–2.3 mm wide, pair of lamellae or ridge towards the apex; pair of globular, waxy calli at the base, 1.1–1.3 mm in diameter. Column erect, narrowly ovate to elliptic, 5–5.5 mm long, 3–3.2 mm wide, apex retuse, pale green-white with light brown colored on both sides, bearing stelidia on either sides and a short foot below; stelidia distinct, falcate, spread out, ca. 4.5 × 1.3 mm, apex acute with a pointed tip, base slightly angled, pale greenish; foot short, 1–1.2 mm long, brown-green; rostellum prominent; stigma located towards the base of the column on a raised, but inclined platform. Anther cap cucullate, ca. 2.2 mm in diameter; pollinia 2, clavate, ca. 2 mm long; ovary obconical, 3.5–3.8 mm long, ca. 2 mm wide, dark brown, verrucose, ribbed. Capsule erect, fusiform, verruculose, ca. 2.5–3.5 cm long, 0.7–0.9 cm wide, dark brown with darker stripes, borne on an elongated pedicel; pedicel with capsule up to 4–8 cm long, brown, slender and terete.

Phenology:— Flowering and fruiting observed during May to December in separate subpopulations. Flowering season of the subpopulations in Samanala Nature Reserve show wide range than the other population in Loolkandura. Flowering and fruiting individuals were observed during May to November at the Samanala Nature Reserve in different years according to the field observations. The Loolkandura subpopulation flowered in December. However, flowering and fruiting individuals were observed simultaneously in same population.

Etymology:— The specific epithet honors Mr. Atthanagoda Kankanamalage Thilakaprema, the second author’s father for his support and guidance.

Distribution:— Gastrodia thilakapremae is endemic to Sri Lanka and occurs throughout sub-montane forest at Kondagala in Loolkandura Estate, Kandy District; in the sub-montane and montane forests of the Samanala Nature Reserve in Central Highlands of Sri Lanka at Galwangediya on Kuruwita–Eratne–Sri Pada trail and Mahagalthalawa on Moray Estate–Sri Pada trail in Ratnapura District ( Fig. 7 View FIGURE 7 ).

Habitat and ecology:— This species is found on montane and sub-montane forests between 1500–2000 m a.s.l and under the shade of Strobilanthes (Acanthaceae) shrubs among the thick leaf litter. Mostly prefers partially open canopy and humus rich soil. Other notable members of Orchidaceae family sharing the same habitat were, Liparis elliptica , Calanthe masuca , Zeuxine sp. and Oberonia sp. in Samanala Nature Reserve. Oberonia scyllae , Peristylus aristatus , Chiloschista fasciata and Phaius wallichii in Kondagala, Loolkandura Estate.

Conservation status:— Gastrodia thilakapremae occurs in both montane and sub-montane forests at 3 different sites in Sri Lanka, one in Kandy District, Central Province and two in Ratnapura District, Sabaragamuwa Province. This species was recorded from Kondagala in Loolkandura Estate in 2012 where it was seen in bloom regularly in 2016, 2018, 2019, 2020, 2021 and 2022 with 4, 6, 2, 11, 5 and 6 individuals respectively ( Fig. 8 View FIGURE 8 ). Two other subpopulations were found in 2020 from Galwangediya area, Eratne–Sri Pada trail and Mahagalthalawa, Moray Estate–Sri Pada trail in Samanala Nature Reserve and both of sites were revisited in 2022. The subpopulation in Galwangediya area, Eratne–Sri Pada trail consisted of 11 mature plants in 2020 and 16 in 2022. Mahagalthalawa subpopulation is the smallest among all with 4 individuals in 2020 and 3 in the following visit in 2022. The habitats of this species in Sri Pada are also threatened due to the clearance of banks and roadsides during the pilgrim season. The population of Kondagala in Loolkandura Estate is faintly protected with a good forest cover but, not safe at all with the human interactions. There is an inferred threat of decline in the quality of habitat. Hence, three sites are considered as three locations. This species may remain dormant with underground tubers, and hence, an optimistic estimate of less than 50 mature individuals has been inferred. The Area of Occupancy (AOO) and the Extent of Occurrence (EOO) were 12 km 2 and ~ 186 km 2 respectively according to GeoCAT ( Bachman et al. 2011). Based on available information this species can be assessed as Critically Endangered (CR D) owing to extremely small population size following IUCN guidelines ( IUCN 2022).

Taxonomic notes:— Gastrodia thilakapremae is morphologically similar with the group of species in Leptogastrodia M.A.Clem & D.L.Jones (≡ Gastrodia ), but differs from all other species by having 55–75 cm tall plant habit; 2.2–2.5 cm long, up to 1.6–1.8 cm wide, dull green color flowers with ovate to rhomboid, 5.5–6.3 mm long, 2.3–4.5 mm wide, orange color labellum and 2.5–3.5 cm long, fusiform capsules.