Schoenorchis mishmensis K. Gogoi, Mega & Chowlu, 2022

Gogoi, Khyanjeet, Mega, Pranab & Chowlu, K., 2022, Schoenorchis mishmensis sp. nov. (Orchidaceae) from Mishmi Hills Lower Dibang Valley District, Arunachal Pradesh, India, Phytotaxa 575 (1), pp. 97-103 : 98-102

Schoenorchis mishmensis K. Gogoi, Mega & Chowlu sp. nov. ( FIG. 1– 3 ).

Type: India, Arunachal Pradesh, Lower Dibang Valley District, Mishmi Hills , 900m, 24 May 2019, K. Gogoi, Mega & Chowlu ARU0001, (holotype: TOSEHIM, Herbarium of the Orchid Society of Eastern Himalaya ; isotype: CNH, Herbarium of the Botanical Survey of India, Kolkata) .

Diagnosis: —The new species is morphologically similar to Schoenorchis brevirachis Seidenfaden (1992: 369) and S. micrantha Reinwardt ex Blume (1825: 362) but differs by the 2.5–7 cm long zig-zag stem, 2.4–4.0 cm long terete leaves, 4–5 densely placed flowers, very short inflorescence (0.4–0.5 cm long), and lip with V shaped callus with mid channel on surface of mid lobe and with raised subglobbose callus on the disc almost covering the spur entrance.

Plant monopodial epiphyte. Roots 2.5–3.5 cm long, 1–1.5 mm in diam., slender. Stems 2.5–7 cm long, 1.2–1.5 mm in diam., usually pendulous, cylindric, zig-zag, somewhat rigid, unbranched, internodes 4.0–7.0 mm. Leaves many, distichous, linear, terete, recurved, 24–40 × 1.0– 1.5 mm, acute, with tubular sheathing at base, glabrous, sessile, fleshy, adaxial grooved. Inflorescences yellowish-white, lateral, raceme, pendulous, 4–5 mm long, bearing 1–2 short, ovate-triangular, obtuse sterile bracts; peduncle ca. 2.0– 2.5 mm long; rachis ca. 2.0– 2.5 mm long, with 4–5 shortly pedicellate flowers; pedicel and ovary ca. 2.0 mm long, ridged, ovary white or pale yellow; floral bracts ca. 0.8 mm, persistent, glabrous, triangular, acuminate. Flowers 4.5–5.0 mm across, successively opening, uniform white, glabrous, sepals & petals connivent. Sepals sub-equal, not spreading; dorsal sepal concave, ovate, ca. 1.5 × 2.0 mm, 1- veined, obtuse, arched over column; lateral sepals slightly obliquely broadly ovate, 2.3 × 1.6 mm, apex obtuse. Petals lanceolate, ca. 1.8 × 1.0 mm, 1-veined, apex acute. Lip spurred, adnate to base of column, immovable, fleshy, concave, 3-lobed; lateral lobes obscure, overlapped the mid lobe; mid-lobe ca. 1.1 × 1.2 mm, ovate, rotund, blunt, entire, concave, V shaped callus with mid channel on surface of mid lobe, with raised subglobbose callus on the disc almost covers the spur entrance, thickly fleshy, apex obtuse; spur parallel to ovary, clavate, ca. 3 × 1.1 mm, obtuse. Column short, thick, ca. 1 mm; anther cap broader than long, white, with 2 gibbose on abaxial; rostellum ca. 0.6 mm; stigma ca. 0.7 mm. Pollinarium with 4 pollinia, appearing as 2 unequal masses, obovate, waxy, yellow, ca. 0.46 mm long; caudicle ca. 1.0 mm, attached by a stipe to a narrowly ovate viscidium.

Flowering: —July–October.

Habitat:— Epiphytic on tree trunks in tropical mixed evergreen forest at 900 m in Mishmi Hills, Lower Dibang Valley District, Arunachal Pradesh.

Distribution:— Only known from India (Mishmi Hills, Lower Dibang Valley District, Arunachal Pradesh).

Etymology:— The specific epithet refers to the Mishmi Hills, Arunachal Pradesh, in North East India where the plant was collected.

Taxonomic notes:˗ Schoenorchis mishmensis is morphologically similar to S. brevirachis and S. micrantha , but distinct from these species in having a short stem 2.5–7 long (vs 12–15 cm long in S. brevirachis and up to 15 cm long in S. micrantha ), with 2.4–4.0 cm long, terete, recurved leaves (vs 2.5–3.5 cm long, semiterete, channelled in S. brevirachis and 3–6 cm long, semiterete, slightly channelled in S. micrantha ); inflorescences 0.4–0.5 cm long, 4–5 flowered only (vs 6.0–8.0 mm long, 6–8 flowered in S. brevirachis and 20–50 mm long, densely many-flowered in S. micrantha ); peduncle 0.2–0.25 cm long; flowers 4.5–5.0 mm across, white (vs 3.0 mm across, violet- red in S. brevirachis and 1.5 mm across, white flushed with pink, slightly hairy in S. micrantha ); with concave lip, lateral lobes overlapped the mid lobe, mid-lobe with V shaped callus with mid channel on surface of mid lobe (vs W shaped in S. brevirachis and longitudinal ridge in S. micrantha ).

Conservation status:— Currently Schoenorchis mishmensis is known only from the type locality where it occurs in a single population containing ca. 20 mature individuals within an area of ca.100 square meters, however, the Area of Occurrence can be estimated as 4 km 2. No anthropogenic activity was observed in the type locality and the only possible threat to these plants was trampling by wild animals. So, the species can be assessed as Critically Endangered based on its small population size ( CR D) following IUCN (2012).

Figures

FIGURE 1. A. Natural habit of Schoenorchis mishmensis. Photos by K. Gogoi.

FIGURE 2. Schoenorchis mishmensis A. Habit. B. Inflorescence. C. Side view of flowers. D. Ventral view of flower. E. Ventral view of perianth. F. Lip with ovary & column. G. Dorsal view of lip. H. Ventral view of lip. I. Longitudinal section of lip. J. Ovary with pedicel and column. K. Front view of Column. L. Ventral view of pollinarium. M. Dorsal view of pollinarium. N. Anther cap dorsal view. Photos by K. Gogoi.

FIGURE 3. Schoenorchis mishmensis A. Habit. B. Inflorescence. C. Side view of flowers. D. Ventral view of flower. E. Ventral view of perianth. F. Lip with ovary & column. G. Dorsal view of lip. H. Ventral view of lip. I. Ovary with pedicel and column. J. Front view of Column. K. Ventral view of pollinarium. L. Dorsal view of pollinarium. M. Anther cap dorsal view. Drawing by K. Gogoi.