Rhomboda obcordata Aver., V.C.Nguyen & Ormerod, 2023

Averyanov, Leonid V., Nguyen, Van Canh, Vuong, Truong Ba, Nguyen, Khang Sinh, Nuraliev, Maxim S., Nguyen, Cuong Huu, Ormerod, Paul A., Maisak, Tatiana V., Diep, Dinh Quang, Lyskov, Dmitry F. & Nong, Duy Van, 2023, New orchids in the flora of Vietnam VII (Orchidaceae: tribes Cypripedieae, Cranichideae, Orchideae, and Collabieae), Phytotaxa 619 (4), pp. 255-276 : 265-269

Rhomboda obcordata Aver., V.C.Nguyen & Ormerod , sp. nov.

( Fig. 4 )

Diagnosis:—The new species differs from the most morphologically close Rhomboda abbreviata , R. confusa , R. lanceolata and R. tokioi mainly in distinctly clawed, obcordate epichile.

Type:— VIETNAM. Lam Dong Province: Dalat Town Area , 2021, Nguyen Van Canh, Nguyen Phi Tam AL 1530 (holotype LE01169157 https://en.herbariumle.ru/?t=occ&id=141035, drawing LE01124110 https://en.herbariumle. ru/?t=occ&id=168555) .

Etymology:—The species name refers to the obcordate shape of the epichile.

Description:—Terrestrial herb with creeping rhizome and ascending leafy floriferous stem. Rhizome fleshy, dull brownish purple, (4)6–8(10) cm long, rooting at nodes. Floriferous stem (26)28–32(34) cm tall, glabrous, with 3–4(5) leaves distant in middle or lower half. Leaves petiolate; petiole and sheath (1.5)2–3(3.5) mm long, 1.5–2 mm wide; leaf blade narrowly ovate, sometimes slightly oblique, obtuse to acute, (3.5)4–7(8) cm long, (1.6)1.8–2.4(2.6) cm wide, entirely glabrous, adaxially velvety dark green to brownish, with white median longitudinal stripe, abaxially uniformly greenish or dull purple. Peduncle erect, (8)10–12(14) cm long, densely shortly hairy, ebracteate or with 1(2) sterile bracts; bracts cuneate, acuminate, (1)1.2–1.5(1.8) cm long, (2)2.5–3(4) mm wide, with entire margin, glabrous; rachis (7)8–9(10) cm long, finely papillose, usually with (8)10–14(16) laxly arranged flowers. Floral bracts herbaceous, dull green, triangular broadly ovate, cymbiform, acute, (5)7–10(11) mm long, (2)2.2–3(3.2) mm wide, with ciliate to finely fimbriate margin, glabrous or subglabrous on both surfaces. Pedicel and ovary dull green, cylindrical, twisted, straight, erect, (0.8)1.1–1.2(1.4) cm long, (1.8)2–2.2(2.4) mm in diameter, glabrous. Flowers not resupinate (or hardly resupinate), hardly opening, (4)4.2–6(6.2) mm long. Sepals subequal, forward directed, narrowly ovate, cymbiform, acute to shortly acuminate, glabrous; median sepal (3.8)4(4.2) mm long, (1.8)2(2.2) mm wide; lateral sepals (4.8)5(5.2) mm long, (2)2.2(2.4) mm wide, slightly oblique. Petals narrowly semi-ovate, oblique, acute to apiculate, 1-nerved, as long as median sepal, 1.2–1.4 mm wide, glabrous, adjacent to the median sepal forming forward directed hood. Lip forward directed, (4.2)4.4–4.6(4.8) mm long, distinctly divided into hypochile and epichile; hypochile concave, with erect lateral lobes, rectangular in outline, 2.4–2.6 mm long and wide (being flattened), with 2 massive globose or broadly conoid glands at base, at middle with 3 keels; epichile obcordate, (0.9)1(1.1) mm long, 1.5–1.6 mm wide, at base with narrow claw 0.9–1 mm long. Column stout, shortly cylindrical, (1.6)1.8–2(2.2) mm tall, about 1.2 mm wide, at apex with 2 short, finger-like, forward directed arms. Anther semi-globose, 0.8–1 mm across, shortly beaked at front. Capsule erect, fusiform, slightly attenuate at apex, 1.4–1.5 cm long, 2.5–3 mm in diameter, opening by 6 slits.

Ecology and phenology:—Evergreen broad-leaved montane forest on granite, likely at elevation of 1400–1500 m a.s.l. Flowers in December–February.

Distribution:—Endemic to Vietnam (Lam Dong Province: Dalat Town Area).

Conservation status:— Rhomboda obcordata is known from a single location where several mature individuals were observed. Pending comprehensive field studies in the area of its locus classicus, we estimate the conservation status of the species as Data Deficient (DD) according to the criteria proposed by the IUCN Standards and Petitions Committee (2023).

Notes:— Rhomboda obcordata is similar to R. tokioi ( Fukuyama 1934: 434) Ormerod (1998: 11) in its habit, leaf color, and the general structure of flower. The new species differs from the latter in obcordate, distinctly clawed epichile (vs. epichile narrowly triangular, tapering from the broad base to the acute apex). Characters sometimes cited for Rhomboda tokioi (Lindley 1840: 491) Ormerod (1995: 329) are due to pollution of some specimens with material of R. abbreviata (type: Nepal, Wallich Cat. no. 7385, K000618044!, shows an obtriangular epichile). The material of R. tokioi seen by us has a subquadrate to shortly broad cuneate epichile without a strongly clawed base.

The new species is also close to R. lanceolata ( Lindley 1857: 186) Ormerod (1995: 329) , differing in the entire obcordate epichile (vs. epichile distinctly bilobulate with elongate lanceolate lobules). In the shape of epichile, R. obcordata resembles the insufficiently known Himalayan R. abbreviata and the Japanese R. confusa Ormerod (1995: 330) , but differs from both in hardly opening small flowers with sepals not more than 5.2 mm long (vs. flowers more or less widely open, with sepals about 7 mm long), narrowly semi-ovate (vs. ligulate, narrowly clawed) petals, and a 3- keeled (vs. 1-keeled) disk. Finally, in its habit and vegetative morphology the new species is indistinguishable from R. petelotii ( Gagnepain 1933: 349) Ormerod (1998: 11) relatively common in Eastern Indochina, which is characterized by velvety dark brownish gray leaves with a white median longitudinal stripe. Rhomboda obcordata is likely a strict endemic of the South Annamese Floristic Region outlined by Averyanov et al. (2003a,b).

Tribe Orchideae (subfamily Orchidoideae )

Habenaria coultousii Barretto (1981: 10) , Chen et al. (2009: 152), Barretto et al. (2011: 244), Hu & Kong (2011: 302), Zhou et al. (2016: 69). Type:— CHINA. Hong Kong SAR: Violet Hill, NW slope, 300 m, 18 October 1978, B.Coultous in G.Barretto 179 (holotype K000796931, isotype HK 34048).

( Fig. 5 )

Ecology and phenology:—Terrestrial tuberiferous ephemeroid herb. Evergreen broad-leaved lowland forests at elevation of 300–400 m a.s.l. Flowers in October–January.

Distribution:— Vietnam (Phu Yen Province: Song Hinh District). Southeast China ( Hong Kong).

Conservation status in Vietnam:—In Vietnam, Habenaria coultousii is known from a single location, where it is locally common, with numerous flowering individuals observed in a small forest area (along a trail several hundred meters long). Pending comprehensive field studies in this area, we estimate the national conservation status of the species as Data Deficient (DD) according to the criteria proposed by the IUCN Standards and Petitions Committee (2023).

Notes:— Habenaria coultousii is reported here as a new record for the flora of Vietnam. This is a rather unexpected discovery, since the species was earlier known as a narrow endemic of Hong Kong. The population found in southern Vietnam morphologically fits well the protologue and the type material, leaving no doubts in the identification. This finding expands the known distribution area of the species by more than 1500 km in the SW direction, with a considerable disjunction.

Surprisingly, H. coultousii looks close in floral morphology to H. amplifolia Cheeseman (1903: 298) endemic to Rarotonga Island ( Cook Islands). Habenaria amplifolia is distributed more than 11000 км ESE of the known locations of H. coultousii . According to the type (K000827058 photo!), description, and illustrations of H. amplifolia ( Cribb & Whistler 2011: 129, fig. 27, 67), it differs from H. coultousii in larger size of plant, larger flowers and longer spur, and especially in much larger leaves 18–29 cm long, 3.8–7 cm wide (vs. leaves 2.5–5.2 cm long, 0.8–1.2 cm wide).

Studied specimens:— VIETNAM. Phu Yen Province: Song Hinh District, Song Hinh Municipality, Song Hinh Protected Forest , forest on slope, elevation of 390 m, 12°47’58’’N 109°00’47’’E, 10 January 2021, M. S. Nuraliev, D. F.Lyskov, A. N.Kuznetsov, S. P.Kuznetsova NUR 3083 ( LE01077932 https://en.herbariumle.ru/?t=occ&id=124834, photos LE01122893 https://en.herbariumle.ru/?t=occ&id=99521) .

Peristylus affinis (D.Don) Seidenfaden (1977: 48, 1992: 49 ), Pearce & Cribb (2002: 174), Schuiteman et al. (2008: 303), Chen et al. (2009: 142), Kurzweil (2010b: 32, 2011: 225, Fig. 130), Rokaya et al. (2013: 540), Jalal & Jayanthi (2015: 37), Zhou et al. (2016: 106), Ormerod et al. (2021: 189) .

( Figs. 1 I–N )

≡ Habenaria affinis D. Don (1825: 25) . Type:— NEPAL. Hab. in Nepalia, Toka, July 1821, Wallich s.n., Wall. Cat. 7066A p.p. (lectotype CAL, designated by Prain in King & Pantling 1898: 327, isolectotype K000247460, fide Pearce & Cribb 2002: 174, Kurzweil 2010b: 32).

Ecology and phenology in Vietnam:—Terrestrial tuberiferous ephemeroid herb. Evergreen broad-leaved montane forest, scrub and grasslands at elevation of 1600–1700 m a.s.l. Flowers in June–July.

Distribution:— Vietnam (Ha Giang Province: Quan Ba District). Nepal, Bhutan, India , Bangladesh, Myanmar, China, Thailand, Laos, Cambodia.

Conservation status in Vietnam:—In Vietnam, Peristylus affinis is known from a single location in the northern part of the country near the Chinese border. According to our observations, it is a rare plant in secondary forest, which provides evidence for the ability of this species to survive in secondary plant communities. Since information about its ecology and distribution in Vietnam is scarce, we assess national status of this species as Data Deficient (DD) according to the criteria proposed by the IUCN Standards and Petitions Committee (2023).

Notes:— Peristylus affinis is reported here as a new record for the flora of Vietnam. This discovery was rather expectable because the species has already been recorded in several countries surrounding Vietnam. Across its global distribution range, it occurs in various types of habitats at elevations of 400–3000 m a.s.l.

Studied specimens:— VIETNAM. Ha Giang Province: Quan Ba District, Cao Ma Po Commune, Vang Cha Phin Village , around point 23°05′22.6′′N 104°49′12.3′′E, at elevation of 1685 m, secondary evergreen broad-leaved forest on silicate mountain, herb about 50 cm tall, flowers white, not common, 6 July 2017, Nguyen Sinh Khang, Nguyen Tien Hiep, Giang Minh Hai NSK 950 ( HN, photos LE01122468 https://en.herbariumle.ru/?t=occ&id=82957) .

Figures

FIGURE 1. Paphiopedilum barbigerum var. barbigerum. A. Flowering plant in natural habitat. B & C. Flowers, front view. Specimen: L.T.Van, K.S.Nguyen AL 1605. Myrmechis urceolata. D. Flattened flowering and fruiting plants. E & F. Apical part of floriferous stem with flowers. G & H. Flowers and flower buds, side and front view. Specimen: T.B.Vuong, N.T.Luan AL 1237. Peristylus affinis. I. Flattened plant. J. Portion of inflorescence. K. Flower, side view. L. Detached flower, side view, with sepals removed. M. Detached flower, sagittal section. N. Detached flattened sepals, petals and lip. Specimen: S.K.Nguyen, T.H.Nguyen, M.H.Giang NSK 950. Photos by L.T.Van & K.S.Nguyen (A–C), T.B.Vuong (D–H) and K.S.Nguyen (I–N); photo correction and design by L.Averyanov and T.Maisak.

FIGURE 4.Rhomboda obcordata. A.Flowering plant.B. Portion of rachis with flower,side view.C.Floral bract, adaxial side.D. Flattened flower. E. Lip, side view. F. Lip, sagittal section. Drawn from the type specimen (V.C.Nguyen, P.T.Nguyen AL 1530) by L.Averyanov and T.Maisak.

FIGURE 5. Habenaria coultousii. A. Flowering plant in nature. B & C. Leafy part of stem. D. Basal part of stem and tubers. E. Portion of stem in its middle part. F. Leaves, adaxial and abaxial side. G. Inflorescences. H & I. Flower, half-side and front view. J. Detached flower, half-side and front view. K. Pedicel and flower, side view. L. Pedicel and flower, back view. M. Spur, side view. N. Column in intact flower, front and half-side view. O. Detached column, views from different sides. P. Anther and rostellum. Q. Auricles (stelidia). Photos by M.S.Nuraliev from the specimen Nuraliev et al. NUR 3083, photo correction and design by L.Averyanov and T.Maisak.