Gastrodia gunatillekeorum Bandara, Priyankara & Kumar, 2020

Bandara, Champika, Priyankara, Theja, Atthanagoda, Anusha G., Lakkana, Tithira, Ediriweera, Sisira & Kumar, Pankaj, 2020, Gastrodia gunatillekeorum (Gastrodieae, Epidendroideae, Orchidaceae), a new species from a lowland rainforest of Sri Lanka, Phytotaxa 436 (1), pp. 55-62 : 56-58

Gastrodia gunatillekeorum Bandara, Priyankara & Kumar , sp. nov. ( Figs. 1–2 )

TYPE: SRI LANKA. Southern Province, Matara District, Sinharaja MAB reserve, above Beverley Estate , 06 April 2018, CB-201804-01 ( PDA!- holotype) ; Sabaragamuwa Province, Rathnapura District, CTFS forest dynamic plot in Sinharaja MAB reserve, 16 March 2019, CB-201903-01 ( PDA!- paratype: spirit)

Diagnosis: Gastrodia gunatillekeorum is close to Gastrodia spatulata , in having white coloured free frontal lobes of the perianth tube and yellow-orange colouration on the inner side of the perianth tube however, the former can be distinguished from latter in having perianth tube formed by fusion of both petals and sepals to almost 2/3 rd of their length with 1/3 rd of the apical lobe broadly ovate and slightly reflexed backwards (against perianth tube made mainly of sepals, with much shorter spathulate to linear petals fused to the sepals only at the base and upper part lying within the perianth tube in latter); labellum rhomboid shaped (against elongate-elliptic); column broadest towards the centre (against broadest towards the apex) and U-shaped stigma (against V-shaped).

Description: Terrestrial, holomycotrophic herbs, 4–7 cm tall. Rhizome tuberous, irregularly-ellipsoid, 7–10 cm long, 1.5–1.8 cm in diam., prostrate, slightly flattened, with hairs dispersed along the gaps between closely placed membranous triangular scales emerging from the nodes. Raceme erect, peduncle 2–5 cm long, glabrous, reddishbrown or purplish-brown in color, with 2–5 membranous semi-transparent sheaths; sheaths tubular, 2.5–3.7 mm long. Inflorescence erect with 3–8 flowers, rachis ca. 3–5 cm long; bracts triangular-ovate, 3.7– 1.8 mm, apex acute dark greyish brown to dark brown, membranous, base surrounding the pedicel. Pedicel dull white, ca. 3.5–4.0 mm long. Flowers resupinate with urceolate perianth tube formed by fusion of sepals and petals, apical part free forming a fivelobed front; perianth tube slightly arched upwards, with 4 ridges, 1.5–2.0 cm long, up to 0.5 cm wide, outer surface light brown to greyish brown, verruculose, inner surface yellowish to light orange in color under lateral sepals and white under dorsal sepal and petals; lobe of dorsal sepal very broadly ovate, 10.0 × 6.5 mm, apex obtuse, slightly convex, pure white, margins entire except serrulate towards the apical half; lobes of lateral sepals broadly obovate, 0.9 × 0.6 cm, margins entire towards base and serrulate towards apical half, pure white except yellowish patch at the base; petal lobes 2, broadly spathulate with base contracted, smaller than sepal lobes, 0.8 × 0.5 cm, pure white; lip adnate to column foot, ovate to rhomboid, 5.0– 5.5 mm long, 3.0– 3.2 mm wide, margin entire, apex acute, slightly tapering, white and yellowish towards apex and along each lateral margin, enclosed within the perianth tube, with a pair of lamellae or short ridge towards the apex and a pair of globular calli at the base near, longitudinally channeled underneath; column erect, ovate with retuse apex bearing stelidia on both sides, 6.0– 6.5 mm long, 3.0– 3.2 mm wide, white in color with light brown colored base from dorsal side and orange in color ventral side; stelidia distinct, narrow like wings, 0.5–0.8 mm long, 0.3–0.5 mm wide, apex triangular to acute; edges parallel to column, base slightly angled, white; rostellum prominent; stigma located towards the lower half of the column on a raised but slightly inclined platform; anther cap hemispheric, ca. 1.5 mm in diameter; pollinia 2, clavate, ca. 1 mm long; ovary obconical, 3.0– 3.5 mm long, ca. 2 mm wide, greyish-brown, ribbed; fruits erect, fusiform, verruculose, ca. 2.0– 2.5 cm long, 0.4–0.5 cm wide, dark brown with much darker stripes, borne on an elongated pedicel; pedicel in fruit, up to 16 cm long, dull white, slender and terete.

Flowering and fruiting: February to April.

Etymology: The species epithet is an eponym in the Latin genitive plural honouring the pioneer forest ecologists of Sri Lanka, Prof. Nimal Gunatilleke and Prof. Savitri Gunatilleke (University of Peradeniya) in appreciation of their dedication and decades of philanthropic work on the forest ecology and conservation in the region.

Habitat ecology: Three distinct populations were found in Western and Southern regions of Sinharaja MAB reserve. All of these populations were always found with thick leaf litter enriched with decaying stumps and stems. In the Southern part of Sinharaja MAB reserve (above Beverley Estate, Deniyaya) one population was discovered and two populations from Western part (CTFS 25 ha forest dynamic plot and above Pitakele, Kudawa) growing in wet soil containing partly-decomposed leaf litter, in very deep shade of the canopy of Mesua -Shorea community dominant lowland rainforest. The climate at all three localities is seasonal and receives precipitation from the Southwest (April–July) and North-east monsoons (October–December), with inter-monsoonal convectional rains. The mean annual rainfall fluctuates between 3750–6000 mm in both Western and Eastern ends of Sinharaja MAB reserve. The mean annual temperature at these sites is 25 ̊C (Ashton, 1992; Gunatilleke et al., 1987).

Taxonomic notes: The new species seems close to fit into the genus Neoclemensia Carr (1935: 180) which was recognized by Pridgeon et al. (2006) and was known to be a monotypic genus represented by a single member N. spatulata Carr (1935: 180) distributed in Borneo and Java ( Govaerts et al. 2019). Neoclemensia was differentiated from Gastrodia on the basis of shield-shaped stigma borne on a raised protuberance at the base of the column in former against oblong or broadly V-shaped stigma borne above the base of the column in latter. However, Wood et al. (2011) considered Gastrodia and Neoclemensia to be conspecific and accordingly merged latter under the former. This treatment was followed by Chase et al. (2015) in the latest classification of family Orchidaceae and later by Suetsugu et al. (2018). However, neither of them gave an explanation to support their merger. The new species, Gastrodia gunatillekeorum looks close to Neoclemensia spatulata which is now called as Gastrodia spatulata , however it can be easily distinguished on the basis of petals being fused to sepals forming a perianth tube together, rhomboid to ovate labellum and column with broad middle part in former against, petals much shorter than the sepals and fused only at the base hence not contributing to the formation of perianth tube, labellum elongate to elliptic and column broader towards the apex in latter.

Prior to the discovery of new species, only one species of Gastrodia namely, G. javanica (1861: 311) was known from Sri Lanka which was reported by George Henry Kendrick Thwaites (1864) in his Enumeratio Plantarum Zeylaniae along with 145 other species of orchids. This treatment was followed by Trimen (1898). However, Schlechter (1906) claimed the Sri Lankan Gastrodia to be distinct from G. javanica and called it G. zeylanica ( Schlechter 1906) . Jayaweera (1981) documented it to be endemic to Sri Lanka, but, his own illustration (fig. 147) belonged to another orchid Didymoplexis pallens . Later based on the illustration of Jayaweera (1981, t. 147), Khan & Halam (1989) reported the occurrence of Gastrodia zeylanica in Bangladesh which was wrong. This treatment was corrected by Fernando and Ormerod (2008).

Now, the genus Gastrodia is represented by two species in Sri Lanka, namely, G. gunatillekeorum and G. zeylanica . Former can be easily distinguished from the latter in having a shorter stature of the whole plant (<10 cm), yellow-orange colouration inside the perianth tube and shorter lip (<6mm) in former against taller stature of the whole plant (> 10 cm), dull white colour inside the perianth tube and longer lip (up to 10 mm) in latter. Both of these species are endemic to Sri Lanka.

There is also a determinavit of Suranjan Fernando of “ Gastrodia dassanayakei Fernando, Wijesundara & Gunasekara ” dated 29.11.2007, on the sheet of Gastrodia zeylanica at PDA (Galle District, Kanneliya, Thawalama forest range, 195 m, 1992, Jayasuriya & Wijesinghe 6388 and Kanneliya, between Nanikita ella and Narangas ella, 400 m, 2003, S.S. 2003-18). Current authors cannot trace the origin of the name, Gastrodia dassanayakei and assume that it was never published. Moreover, the first sheet is holotype of G. zeylanica and the plant on the second sheet matches well with the plant first.

Conservation assessment: The distribution of Gastrodia gunatillekeorum appears to be restricted to lowland tropical rainforests in Sri Lanka. Three distinct populations were observed in Western part and Southern part of Sinharaja MAB reserve. First population had around 40 mature individuals in Deniyaya spread over approximately 500 square meters; second population with around 20 mature individuals at the CTFS site covering approximately 1000 square meters; third population with 5 mature individuals in Pitakele, spread over an approximate area of 100 square meters. All populations were found at an elevation of around 400– 610 m. All three population sites were also associated with one or few other mycotrophic species namely, Thismia gardneriana Hook.f. ex Thwaites (1864: 325) : Critically Endangered, Burmannia championii Thwaites (1864: 325) : Endangered and Aphyllorchis montana Reichenbach (1876: 57) : Vulnerable (conservation status as per National redlist of Sri Lanka ( MOE 2012). These mycotrophic plants are known to be highly specific in their mycorrhizal associations and hence specific to their habitat too ( Jacquemyn et al. 2016). Hence with the occurrence of so many mycotrophic plants, the habitat must be very important and unique. The forest of Deniyaya is bordered with tea plantations, but the habitat of new species is located in primary forest area that lies few hundreds of meters inside from border. Pitakele area was threatened due to timber harvesting by the State Timber Corporation in 1972–1977 ( Sri Bharathie 1979) but after the banning of cutting of trees, the forest has recovered and already exhibiting some characteristics of primary forests. This area is now protected under Forest Department of Sri Lanka. It is possible that G. gunatillekeorum occurs in adjacent areas that have not yet been fully explored. Based on current knowledge, the Extent of Occurrence (EOO) and Area of Occupancy (AOO) was estimated using GeoCAT ( Moat 2007) as ~ 48 km 2 and 12 km 2 respectively. With 3 small populations, comprising less than 100 mature individuals, the species can be assessed as Endangered (EN: D) based on latest IUCN guidelines ( IUCN 2019).

Additional specimens examined: Burmannia championii :—KALUTARA DISTRICT: Kalutara forest reserve (approach Addaragoda Southern slopes), 125 m, 1993, Jayasuriya & Wijesinghe 7238 (PDA!); RATNAPURA DISTRICT: Pitakele, Sinharaja, 2017, CB 46 (PDA!). Gastrodia zeylanica :—GALLE DISTRICT: Kanneliya, Thawalama forest range, 195 m, 1992, Jayasuriya & Wijesinghe 6388 (PDA!); Kanneliya, between Nanikita ella and Narangas ella, 400 m, 2003, S.S. 2003-18 (PDA!). Thismia gardneriana :—RATNAPURA DISTRICT: Pitakele, Sinharaja, 2017, CB 45 (PDA!).

Figures

FIGURE 1. Gastrodia gunatillekeorum Bandara, Priyankara & Kumar sp. nov. A. Plant (CB-201804-01-Holotype). B. Flowering plant. C. Front view of flower. D. Lateral view of flower. E. Dorsal view of flower. F. Flower bud with bract. G. Side view of lip and column. H. Ventral view of column. I. Dorsal view of lip. J. Dorsal view of column. K. Ventral view of lip. L. Capsule. M. Tuberous rhizome (Scale bar = A–F 10 mm; G–K 5 mm; L,M 10 mm). Photographs by Champika Bandara (A–L) and Anusha G.Atthanagoda (M).

FIGURE 2. Gastrodia gunatillekeorum Bandara, Priyankara & Kumar sp. nov. A. A flowering plant. B. Lateral view of flower. C. Dorsal view of flower. D. Front view of flower. E. Side view of lip and column. F. Ventral view of lip. G. Dorsal view of lip. H. Ventral view of column. I. Dorsal view of column. J. Dorsal view of anther cap. K. Ventral view of anther cap. L. Pollinia. M. Plant with fruits. N. Close up of fruit. Illustrations by Champika Bandara and Pankaj Kumar.