Taiwania 65(4): 478‒492, 2020 DOI: 10.6165/tai.2020.65.478 

New Orchids in the Flora of Vietnam III (Collabieae, Malaxideae, Nervilieae and Orchideae) 

Leonid V. AVERYANOV1,*, Ba Vuong TRUONG2,3, Van Canh NGUYEN4, Tatiana V. MAISAK1, Quang Diep DINH4, Maxim S. NURALIEV5,6, Khang Sinh NGUYEN7, Van Tan CHU8 

1. Komarov Botanical Institute of the Russian Academy of Sciences, Prof. Popov Street 2, 197376, St. Petersburg, Russia.

2. Institute of Tropical Biology, Department of Biological Resources, Vietnam Academy of Science and Technology, Tran Quoc 

Toan Street 85, District 3, Ho Chi Minh City, Vietnam. E-3. 

3. Graduate University of Science and Technology, Vietnam Academy of Science and Technology, Hoang Quoc Viet Road 18, Nghia 

Do, Cau Giay District, Hanoi, Vietnam. E-mail: bavuong2019@yahoo.com 

4. Institute of Applied Technology, Thu Dau Mot University, Tran Van On Street 6, Phu Hoa Ward, Thu Dau Mot City, Binh Duong 

Province, Vietnam. E-mail:VCN: nguyenvancanh@tdmu.edu.vn; QDD: dinhquangdiep@tdmu.edu.vn 

5. Joint Russian-Vietnamese Tropical Scientific and Technological Center, Cau Giay, Hanoi, Vietnam. 

6. Department of Higher Plants, Biological Faculty, M.V. Lomonosov Moscow State University, Leninskie Gory 1, 12, 119234, 

Moscow, Russia. E-mail: max.nuraliev@gmail.com

7. Institute of Ecology and Biological Resources, Vietnam Academy of Science and Technology, Hoang Quoc Viet Road 18, Nghia 

Do, Cau Giay, Hanoi, Vietnam. E-mail: khangnguyensinh@yahoo.com

8. The Center for Rescue and Conservation of Organism, Sa Pa District, Lao Cai Province, Vietnam. Corresponding author’s email: av_leonid@mail.ru or av_leonid@yahoo.com 

(Manuscript received 27 August 2020; Accepted 28 September 2020; Online published 6 October 2020) 

ABSTRACT: The paper presents new data on the orchid diversity in Vietnam obtained in 2016–2020. It contains descriptions of one genus (Apetalanthe) and two species new to science (Apetalanthe gracilis, Nervilia appressifolia), as well as one genus (Neottianthe) and four species (Calanthe tricarinata, Collabium yunnanense, Dendrobium praecinctum, Neottianthe secundiflora) new for the flora of Vietnam. Apetalanthe is particularly remarkable for the reduction of petals. The accepted name, synonyms, type, citations of relevant regional taxonomic publications, data on ecology, phenology and distribution, estimated IUCN Red List status, studied specimens, brief taxonomic notes, and illustrations are provided for each recorded species. 

KEY WORDS: Indochina, nature protection, new genus, new species, new records, orchids, plant geography, plant taxonomy. 

INTRODUCTION 

This paper continues the successive publication of new data on the orchid diversity in Vietnam (Averyanov et al., 2018a–g, 2019a–f; Gruss et al., 2019, 2020; Nguyen et al., 2020a, b) obtained in 2016–2020. Similar to the previous papers, it summarizes the results of joint efforts of professional botanists and orchid enthusiasts on studies of the Vietnamese native orchids. We report here one genus, Apetalanthe and two species new to science, Apetalanthe gracilis (Orchideae, Orchidinae), Nervilia appressifolia (Nervilieae, Nerviliinae), as well as one genus, Neottianthe and four species, Calanthe tricarinata, Collabium yunnanense (Collabieae), Dendrobium praecinctum (Malaxideae, Dendrobiinae) and Neottianthe secundiflora (Orchideae, Orchidinae) new for the flora of Vietnam. In the suprageneric classification we followed the most recent taxonomic treatment of the orchid family proposed by M.W. Chase et al. (2015). The accepted plant name, synonyms, type, citations of relevant regional taxonomic publications, data on ecology, phenology and distribution, estimated IUCN Red List status, studied specimens, brief taxonomic notes, and illustrations are provided for each recorded species. 

MATERIALS AND METHODS 

Voucher specimens and photo materials cited here were obtained during the years 2016–2020. Collected plants, inflorescences and flowers were herbarized directly or fixed and stored in 60–65% ethanol prior to preparation of herbarium specimens. In the descriptions of quantitative characters, infrequent extreme values (i.e. rarely occurring minimal and maximal values) of a variation range are parenthesized before and after the normal variation range. Detailed analytical photos of plant parts were made from the living or liquid-preserved plants prior to preparation of the voucher herbarium specimens. In the citation of the taxa distribution in Vietnam, including the provinces, we follow the modern official administrative division of the country (Vietnam Administrative Atlas, 2015; Provinces of Vietnam, 2019). The online version of the IUCN Red List of Threatened Species (2016) was used for tentative estimation of species conservation status. Place of the housing of cited specimens is indicated by internationally accepted herbarium acronyms (Thiers, 2020). The studied specimens are available in the database of the LE Herbarium (http://en.herbariumle.ru). 

The studied taxa are listed below in alphabetical order. 

TAXONOMIC TREATMENT 

List of new orchids in the flora of Vietnam 

Apetalanthe Aver. & Vuong, gen. nov. (Orchideae: Orchidinae) 

Type: A. gracilis Aver. & Vuong 

Diagnosis. The new genus differs from the most morphologically close genera Orchis L. and Ponerorchis Rchb.f. in the emarginate median sepal, visual absence of petals (completely reduced or fused with median sepal), naked viscidia without bursicle and large swelling rostellum hanging above stigma. Monotypic genus. Etymology. The name of the genus refers to its apetalous flowers.

A. gracilis Aver. & Vuong, sp. nov. 

Fig. 1–3 Described from NW Vietnam. Type: VIETNAM, Lao Cai Province, Fansipan Mountain, 23 June 2019, Truong Ba Vuong, Nguyen Thanh Luan, AL 1238 (holotype - LE 

LE01076866, http://en.herbariumle.ru/?t=occ&id=18974; photo of living plant prior to preparation of holotype, LE LE01061298, http://en.herbariumle.ru/?t=occ&id=12492; drawing of the type specimen, LE LE01087235, http://en.herbariumle.ru/?t=occ&id=18950). 

Description. Herb terrestrial or lithophytic, tuberiferous, stoloniferous, generally glabrous. Tuber underground, subglobular, ovoid or shortly cylindrical, pale yellowish to light brownish, (4)4.5–7(8) mm long, densely covered with root hairs; tuber of the next generation developing at the apex of underground terete whitish stolon (4)5–10(or more?) mm long and 1–1.2 mm in diameter. Roots (0)1–2, at base of stem, short and fleshy, hairy. Stem arising from tuber, ascending, oblique or erect, (3.5)4–8(9) cm tall, (0.8–)1(–1.2) mm in diameter, white at base, grassy green in distal half, with fine longitudinal papillulose ribs, at base bearing 3– 4 tubular white or light greenish bracts 3–12 mm long and 1.4–1.8 mm wide (when flattened) with obtuse or acute apex, at middle with 1 suberect or horizontally recurved cauline leaf. Leaf sessile, narrowly lanceolate, often slightly falcate, conduplicate, uniformly grassy green, (2)2.5–3(3.5) cm long, (2.5)3–4(4.5) mm wide, tapering from wide base to obtuse apex, finely papillulose along margin, abaxially with prominent median vein. Inflorescence a terminal lax somewhat secund spike with (1)2–3 flowers; peduncle ebracteate, grassy green, (1.8)2–2.2(2.4) cm long; rachis grassy green, (0.8)1–1.8(2) cm long. Floral bracts leaf-like, narrowly to broadly lanceolate, horizontally recurved, grassy green, (8)12–15(17) mm long, (2.5)3–4(4.2) mm wide, tapering from broad base to acute apex, papillulose along margin. Flowers distant with 6–8 mm between them on rachis, sessile, resupinate, widely opening, white with lip bearing 7 longitudinal purple stripes along veins and at spur base, (7.5–)8(–8.5) mm across. Median sepal erect, 3-veined, broadly ovoid, cymbiform, (2.8)3– 3.2(3.3) mm long, (3.7)3.8–4(4.1) mm wide (when flattened), obscurely 4-dentate and cucullate at apex, sparsely papillulate abaxially and along margin, embracing column. Lateral sepals reflexed or recurved, 1-veined, obliquely narrowly obovate, (3.9)4–4.2(4.3) mm long, (1.9–)2(–2.1) mm wide, blunt to rounded at apex, papillulate along margin. Petals absent during flowering. Lip horizontal to downwards directed, 7- veined, spurred, broadly obovate, almost flat, (5.8)6– 6.5(6.7) mm long, (5.7)5.8–6.2(6.3) mm wide, with 2 small ovoid papillulose transversal calli at entrance of spur, 3-lobed at apex; lobes broadly triangular, 1–1.2 mm long, 2–2.2 mm wide, finely denticulate or irregularly serrulate along margin; spur at right angle to lip, horizontal or upward directed, narrowly cylindrical- conical, straight to slightly curved upwards, obtuse, as long as ovary, (6.3)6.5–7(7.2) mm long, (1.4)1.5–1.8(1.9) mm broad at base, papillulose inside. Column erect, stout, (1.9)2–2.2(2.3) mm tall, 1–1.2 mm wide; anther erect, 1– 1.2 mm tall, with 2 broad parallel, adjacent thecae narrowing at base into short tubes embracing caudicles; viscidia 2, exposed (lacking separate or common bursicle), each viscidium between narrowly acute erect teeth of large swelling hemispheric lateral rostellum lobes; auricles broadly conoid, finely verruculose; stigma entire, rectangular lunate, slightly concave to almost flat, as wide as rostellum, placed below rostellum, facing to broad, almost circular spur entrance. Pollinarium clavate, consisting of sectile pollinium with numerous massulae, short fleshy terete caudicle and ovate to almost circular viscidium at base. Ovary straight to recurved, grassy green, terete to fusiform, (5.5)6–8(10) mm long, (1.4)1.5–1.8(2) mm in diameter, with longitudinal papillulose ribs. Fruit a fusiform capsule. 

Etymology. The species name refers to the slender and elegant plant appearance. 

Habitat, phenology and conservation status. 

Terrestrial and lithophytic tuberiferous herb. Wet mossy open places on rocky outcrops in humid evergreen broad-leaved forest between 2000 and 3000 m a.s.l. Very rare. Flowers in June–July, fruits in August–September. Estimated IUCN Red List conservation status: DD. 

Distribution. NW Vietnam (Lao Cai Province, Hoang Lien Son Range, Fansipan peak area). Endemic to NW Vietnam. Only known from the one location. 

Notes. The new genus is apparently close to Orchis 

L. and Ponerorchis Rchb.f. ( = Chusua Nevski) in plant habit and general floral morphology. Superficially, it particularly resembles some forms of the rare Himalayan taxon, Orchis chusua var. nana King & Pantl. (= Ponerorchis nana (King & Pantl.) Soó). However, our plant differs from all representatives of Orchis and Ponerorchis in emarginate median sepal (vs. median sepal round, obtuse or acute, but never emarginate), absence of petals (vs. petals well developed, as long as sepals and entirely free from them), presence of 2 small ovoid transversal calli at entrance of spur (vs. lip lacking swellings at entrance of spur), viscidia exposed and lacking a bursicle (vs. viscidia covered by 2 separate bursicles or 1 common bursicle), and large fleshy hemispheric rostellum as large as stigma, situated above stigma at the base of the anther and bearing at apex 4 narrowly pyramidal acute erect teeth (vs. rostellum mostly represented by its median lobe forming more or less prominent fold placed between the bases of thecae and forming distally 2 rostellar arms). The mentioned combination of morphological characters is unique and was not observed in any members of other related Asian Orchis-associated genera, like Amitostigma Schltr., Hemipilia Lindl., Hemipiliopsis Y.B.Luo & S.C.Chen, Neottianthe Schltr., and Tsaiorchis Tang & F.T.Wang. Such characters as emarginate median sepal, visual absence of petals and swelling globular rostellum are apomorphies observed only in the discovered plant. 

It is noteworthy that an orchid with similar modification of perianth is currently accepted (Chase et al., 2015) as the monotypic genus Steveniella Schltr. (comprising the species S. satyrioides (Spreng.) Schltr., distributed in Iran, Turkey, the Caucasus and the Crimea). The reduction in the number of perianth segments in Steveniella is caused by the fusion of all three sepals into a synsepalum with the formation of a broad hood, whereas in Apetalanthe the petals are apparently absent (or fused with median sepal). 

A possible interpretation of the perianth of Apetalanthe is the complete union of the petals with the median sepal. The presence of three vascular traces in the median sepal of Apetalanthe makes this organ similar to the lip of many Orchidaceae (Rudall, Bateman, 2002; Rudall et al., 2013). As it has been argued by Rudall et al. (2013) with respect to the three-traced lip, the hypothesis of the compound lip nature (implying a union of the median petal with two outer staminodes) can hardly be endorsed or refuted at the current state of knowledge. In the same way, the idea of the union of the petals with the median sepal in Apetalanthe rather than their complete reduction cannot be discarded. 

The ecology and distribution of Apetalanthe in Vietnam are probably very similar with those of another regional endemic from the same subtribe, the monotypic genus Tsaiorchis Tang & F.T. Wang. 

Apetalanthe gracilis is a rare highland orchid currently known only from the area of Fansipan peak. Consequently, its conservation status may be assessed as “Data Deficient” (DD) following the IUCN Red List terms and criteria. Meanwhile, it is probable that this species inhabits some other high peaks of Hoang Lien Son Range including its NW extension in SE Yunnan (China). The discovered plant represents the ninth genus of Orchidaceae endemic (and subendemic) to Vietnam along with Ascocentropsis Senghas & Schildh., Bidoupia Aver., Ormerod & Duy, Cleisostomopsis Seidenf., Eparmatostigma Garay, Hayata Aver., Lockia Aver., Vietorchis Aver. & Averyanova and Zeuxinella Aver. Similar to all these genera, the newly discovered plant deserves special attention for its conservation as a local endemic of a high taxonomical rank having very limited distribution. 

Calanthe tricarinata Lindl. 1833, Gen. Sp. Orchid. Pl.: 252; Su Horng-Jye, 2000, Fl. Taiwan 5: 790, photo 94; Pearce, Cribb, 2002, Orchids of Bhutan: 291, fig. 65, pl. 11; Chen et al., 2009, Flora of China 25: 297, fig. 426; Clayton, Cribb, 2013, Genus Calanthe: 148, fig. 47, pl. 21A, B; Rokaya et al., 2013, Nord. J. Bot. 31: 519; Lin et al., 2016, Taiwania 61, 2: 86; Zhou et al., 2016, Phytotaxa 276: 25. 

Fig. 4 

Described from Nepal (“Lindl. in Wall. Cat. no 7339 in Hab. in Napalia”). Type – “7339 Calanthe tricarinata Lindl. Napalia 1821 Calanthe ecalcarata, Wall. Monthes vallii Napalia Julio 1821 fl.” (K – K001127196 http://specimens.kew.org/herbarium/K001127196). 

Habitat, phenology and conservation status (in Vietnam). Terrestrial herb. Primary humid evergreen broad-leaved montane forest on granite at elevations of 2000–2500 m a.s.l. Flowers in June–July. Rare. Estimated IUCN Red List status: DD. 

Distribution. NW Vietnam (Lao Cai Province, Fansipan Mountain). Bhutan, Nepal, NE India, Pakistan, N Myanmar, Thailand, mainland China, Korea, Taiwan, Japan. 

Notes. This species is a typical element of the subtropical and warm temperate flora of mainland Asia. Its discovery in Vietnam extends its known distribution area to the highland regions of northern Indochina situated within the tropical latitudes. Studied plants from Vietnam slightly differ from the typical C. tricarinata by the very small keel or plate on the lip disc and can represent a separate variety. 

Studied specimen. NW Vietnam, Lao Cai Province, Fansipan Mountain, 22 June 2019, Truong Ba Vuong, Nguyen Thanh Luan, AL 1234 (LE LE01066670 http://en.herbariumle.ru/?t=occ&id=12428). 

Collabium yunnanense Ormerod, 2013, Taiwania 58(1): 22, fig. 2. 

Fig. 5 

Described from southern China, Yunnan (“Lushui Xian, Luobenzhuo Xiang, E’ga Cun, on forest road at km 30, E side of Gaoligongshan, 2200 m”). Type – “9 Aug 2005, Gaoligong Shan Biodiversity Survey, H. Li et al., 25814” (holotype – CAS). 

Habitat, phenology and conservation status (in Vietnam). Terrestrial and lithophytic creeping herb. Primary evergreen broad-leaved montane forests, swampy and cloudy highland thickets on granite and sandstone at elevations of 1700–1900 m a.s.l. Flowers in May–June. Not common. Estimated IUCN Red List status: DD. 

Distribution. NW Vietnam: provinces Lao Cai (Bat Xat District, Bat Xat Nature Reserve) and Son La (Moc Chau District, Pha Luong Mountain). S China (Yunnan Province). 

Notes. This species, which was described after the publication of the “Flora of China” (Chen et al., 2009), is readily distinguishable from the closely related Collabium chapaense (Gagnep.) Seidenf. & Ormerod and C. formosanum Hayata by a short column and the lower lip portion with two thick fleshy keels interposed apically by a short transverse keel-like callus (Ormerod, 2013). In China, C. yunnanense was reported as an epiphytic plant growing in subtropical forest on granite at an elevation of 2200 m a.s.l. This unattractive, rarely flowering plant probably has a wide distribution in highland areas of NW Vietnam, but is not yet well documented by herbarium collections. 

The protologue of C. yunnanense (Ormerod, 2013) is illustrated only with a drawing. Here, we publish the analytical photos of this species for the first time. 

Studied specimens. NW Vietnam, Son La Province, Moc Chau District, Chieng Son Commune, Pha Luong Village, primary cloud evergreen broad-leaved forest on flat Pha Luong Mountain summit composed with eroded red-brown sandstone at an elevation of 1750–1850 m a.s.l. around point 20°40’23.0N 104°37’52.0E, creeping terrestrial and lithophytic herb on shady mossy boulders, not common, 23 September 2016, L.Averyanov, N.T.Hiep, N.S.Khang, C.Q.Ngan, T.V.Maisak, N.T.Son, CPC 8001 (LE LE01055650 http://en.herbariumle.ru/?t=occ&id=7320); additional herbarium specimens prepared on 13 May 2019 by L. Averyanov and T. Maisak, CPC 8001a, flowers odorless, tepals grassy green, lip white with small sparse deep purple marks, column and anther white (LE LE01055080 http://en.herbariumle.ru/?t=occ&id=5561, LE LE01055649 http://en.herbariumle.ru/?t=occ&id=7319); Plate – d-EXSICCATES OF VIETNAMESE FLORA 0358 / CPC 8001a (Fig. 4, LE LE01087362 http://en.herbariumle.ru/?t=occ&id=30039). Lao Cai Province, Bat Xat District, Bat Xat Nature Reserve, 4 km SSE of Y Ty Village, disturbed swampy forest, 22°37'30''N 103°37'28''E, elevation 1840 m, Nuraliev M.S. 2659, 7 June 2019 (LE LE01059480 http://en.herbariumle.ru/?t=occ&id=10036, LE LE01058723 http://en.herbariumle.ru/?t=occ&id=9376; MW). 

Dendrobium praecinctum Rchb.f. 1877, Gard. Chron., n.s., 7: 750; Seidenfaden, 1995, Opera Bot. 124: 28; Pearce, Cribb, 2002, Orchids of Bhutan: 416, pl. 23; Jin Xiao-Hua et al., 2010, Acta Bot. Yunnan. 4: 333; Zhou et al., 2016, Phytotaxa 276: 50. Origin of the type unknown. Type – “cult. Veitch” (W – Herb. No. 39641). 

Fig. 6A-C 

= Dendrobium pauciflorum King & Pantl. ex King, 1896, J. Asiat. Soc. Bengal, Pt. 2, Nat. Hist. 64: 332; King & Pantl., 1898, Ann. Roy. Bot. Gard. Calcutta 8: 54, pl. 76; Seidenfaden, 1985, Opera Bot. 83: 97, fig. 57, pl. 12C. 

Described from NE India (“Sikkim above Engo, at an elevation of about 4,000 feet; in flower in June.”). Type not located (CAL?). 

Habitat, phenology and conservation status (in Vietnam). Epiphyte on tall trees. Evergreen broad- leaved montane forests. Flowers in June–July. Very rare. Estimated IUCN Red List status: DD. 

Distribution: Vietnam (NW: Lai Chau Province; in addition one unlocalised specimen from the country). Bhutan, NE India, N Myanmar, N Thailand, S China (Yunnan Province). 

Notes. With respect to its distribution, D. praecinctum is a typical East Himalayan species. The discovered locations of this species in Vietnam represent the southeastern limit of its distribution. 

Studied specimens. Vietnam, sine loc., cult. in Pleicu Town, 21 July 2016, Cong Danh Vo, s.n. (LE photo LE01087334 http://en.herbariumle.ru/?t=occ&id=28548). NW Vietnam, Lai Chau Province, 29.06.2020, Nguyen Van Canh, s.n. (LE photo LE01087080 http://en.herbariumle.ru/?t=occ&id=18174). 

Neottianthe secundiflora (Kraenzl.) Schltr. 1919, Repert. Spec. Nov. Regni Veg. 16: 291; Pearce, Cribb, 2002, Orchids of Bhutan: 172; Chen et al., 2009, Flora of China 25: 132, fig. 178 (12–15); Rokaya et al., 2013, Nord. J. Bot. 31: 537; Jalal, Jayanthi, 2015, Lankesteriana 15, 1: 34; Zhou et al., 2016, Phytotaxa 276: 93. 

Fig. 6D-H 

≡ Peristylus secundiflorus Kraenzl., 1898, Orchid. Gen. Sp. 1: 518. ≡ Ponerorchis secundiflora (Kraenzl.) X.H. Jin, Schuit. & W.T. Jin, 

2014, Molec. Phylogen. Evol. 77: 51. 

≡ Habenaria secundiflora Hook.f., 1890, Fl. Brit. India 6: 165; id., 1895, Icon. Pl. 24, tab. 2321, nom. illeg., non Barbosa Rodr., 1881. Described from the Himalayas (“Subalpiner Teil des Himalaya, 3000–3300 m; ... Sikkim 4400 m; ... Chumbi”). Syntypes – NW India, Kumaon, J.F. Duthie 3421 (K000796374 https://apps.kew.org/herbcat/getImage.do?imageBarcode=K0007 96374); NE India, Sikkim, Hooker 278 (K000974209 https://apps.kew.org/herbcat/getImage.do?imageBarcode=K0009 74209); China, Tibet, Chumbi, Dungboo s.n. (K000796373 https://apps.kew.org/herbcat/getImage.do?imageBarcode=K0007 96373). 

Habitat, phenology (in Vietnam) and conservation status. Terrestrial tuberiferous herb. Open mossy and grassy slopes in humid evergreen broad-leaved montane forest at elevations of 2000–3000 m. Flowers in June– July. Very rare. Estimated IUCN Red List status: DD. 

Distribution. NW Vietnam (Lao Cai Province, Fansipan Mountain). Bhutan, Nepal, N India, N Myanmar, 

S China (Sichuan, Yunnan, Xizang provinces).

Notes. Neottianthe secundiflora in its distribution and ecology is a typical species of the subalpine subtropical zone of the high Himalayas. The remarkable discovery of this species in Vietnam considerably expands its known distribution area in the SE direction. This fact also provides an additional evidence for the not yet fully uncovered richness of the flora of the highest mountain peaks of NW Vietnam in subtropical and temperate floristic elements. In this connection, such highland areas play a role of unique disjunctive refuges of subtropical and temperate plant species within the tropical latitudes. 

Studied specimen. Vietnam, Lao Cai Province, Fansipan Mountain, 23 June 2019, Truong Ba Vuong, Nguyen Thanh Luan, AL 1239 (LE LE01066673 http://en.herbariumle.ru/?t=occ&id=12431). 

Nervilia appressifolia Aver. & V.C. Nguyen, sp. nov. Figs. 7-9 Described from S Vietnam. Type: VIETNAM, Dak Lak Province, Yok Don National Park, open dipterocarp forest and woodlands with low bamboo at elevations of 200–300 m a.s.l., terrestrial tuberiferous herb in seasonally flooded and wet soil, very rare, 7 June 2019, Nguyen Van Canh, AL 1109 (holotype – LE LE01076868, http://en.herbariumle.ru/?t=occ&id=19023). Photos of living plants used for the preparation of the type specimen - LE LE01087399 (http://en.herbariumle.ru/?t=occ&id=38798). Photos of liquid preserved specimen and floral parts used for the preparation of the type specimen – LE LE01087291 

(http://en.herbariumle.ru/?t=occ&id=19013).

Etymology. The species name refers to the leaf blade tightly appressed to the ground.

Description. Herb ephemeroid, terrestrial, tuberiferous, stoloniferous, leafless at anthesis, forming leaves after flowering, glabrous. Tuber underground, globular, (4.5)5–6(6.5) mm in diameter, annually substituting, with few short finger-like outgrowths, producing stem at base. Stem underground, erect or suberect, sparsely verruculose, ebracteate, (7)9–18(20) mm long, (0.9)1–1.1(1.2) mm in diameter (in liquid preserved material); at anthesis bearing a terminal peduncle and a lateral vegetative bud covered by 1–2 small scarious bracts; after anthesis bearing a single leaf, epigeous stolons and infructescence (when fruits are developed). Hypogeous stolons arising from tuber outgrowths or from underground portion of stem, white, (3)4–10(14) mm long, about 1 mm in diameter, forming at apex a tuber of an individual plant of the next generation. Epigeous stolons horizontal, creeping, appressed to the ground, light greenish, up to 12 cm long, 0.8–1 mm in diameter, forming new plants at nodes. Leaves sessile or subsessile, with petiole less than 1.5 mm long; leaf blade cordate to orbicular or reniform, convex, umbrella-shaped, (1.2)1.5–2.4(2.6) cm in diameter, blunt or broadly obtuse at apex, margin entire, with 5–11(13) arcuate main veins, tightly appressed to the ground. Inflorescence 1-flowered; peduncle erect, pale olive greenish, (3.5)4–6(6.5) cm long, (0.8)0.9– 1(1.1) mm in diameter, at middle with 1–2 broad tubular obtuse scarious sterile bracts (5)7–12(14) mm long, 2–3 mm wide (when flattened); floral bracts inconspicuous, broadly triangular, less than 1 mm long. Flowers nutant, not widely opening. Sepals and petals subsimilar, broadly lanceolate or narrowly elliptic, shallowly cymbiform, almost straight, pale olive greenish, (7.5)7.8–8.2(8.4) mm long, (1.6)1.8–2(2.2) mm wide, acute at apex, 3-veined. Lip 3-lobed, pandurate in outline, (7.8)8–8.2(8.4) mm long, (2.4)2.6–2.8(3) mm wide; side lobes narrowly rectangular or narrowly obtriangular, erect and embracing column, green, 3–3.4 mm long, 0.7– 0.8 mm wide, obtuse or blunt at apex; median lobe obovate, conduplicately folded, (3.4)3.6–4(4.2) mm long, (2.4)2.6–2.8(3) mm wide (when flattened), apex blunt to roundish, white and sparsely speckled with purple, on adaxial surface bearing a fleshy papillose longitudinal ridge, its proximal part forked into 2 low keels running to middle of hypochile; lip abaxially with narrow longitudinal groove running along almost its entire length. Column simple, erect, stout, clavate, dorsally prominently gibbous, light greenish, (4.2)4.4–4.5(4.6) mm long, 1.2–1.4 mm wide; anther cap helmet-shaped, subquadrate at front view, white to light pinkish, 0.8–0.9 mm long and wide; stigma concave, triangular obovate; rostellum inconspicuous, in form of two lateral horizontal teeth meeting above stigma. Ovary ovoid, olive brown, (2)2.2–2.5(2.6) mm long, (1.2)1.4–1.5(1.6) mm in diameter, shallowly longitudinally grooved. Fruit unknown. 

Habitat, phenology and conservation status. 

Terrestrial tuberiferous ephemeroid herb growing on wet lateritic soil at the bottom of small occasionally flooded (during torrential rains) puddles in open semideciduous seasonally flooded dipterocarp forest and woodland with domination of small bamboo, at elevations of 200–300 m a.s.l. Flowers in May–June. Very rare. Estimated IUCN Red List status: DD. 

Distribution. S Vietnam (Dak Lak Province, Yok Don National Park). Endemic to S Vietnam. 

Notes. The discovered plant belongs to a group of species of the genus Nervilia with 1-flowered inflorescence and 3-lobed lip more or less hairy or papillulate in the center. In mainland Asia this group is represented by N. calcicola Kerr, N. infundibulifolia Blatt. & McCann, N. punctata (Blume) Makino and N. viridiflora Q. Liu & J.W. Li. Among them, the new species is closest in its floral morphology to N. viridiflora which is endemic to southern Yunnan (Tang et al., 2018), but differs in smaller floral bract less than 1 mm long (vs. 5–6 mm long), smaller, nutant, not widely opening flowers with sepals and petals 7.5–8.4 mm long (vs. flowers larger, suberect, widely opening, with sepals and petals 13–18 mm long), lip with obovate or narrowly obovate, obtuse median lobe, as wide as or narrower than the hypochile (vs. median lobe orbicular, emarginate, broader than the hypochile), conduplicately folded (vs. almost flat) lip, and median lobe of the lip with conspicuous tall papillose ridge (vs. median lobe with two insignificant low glabrous keels). At the same time, N. appressifolia strikingly differs from almost all known congeners in the sessile leaf tightly appressed to the ground, long green epigeous stolons and in its habitat at the moist bottom of temporary flooded puddles. Such narrow ecological preferences are not found in any other known species of the genus. 

Nervilia appressifolia is presently known exclusively from a very limited area in Yok Don National Park in Dak Lak Province of southern Vietnam. 

The observed population occupies an area of not more than 500 m2. The attribution of a conservation status to this very rare plant in terms and criteria proposed by IUCN Red List requires additional field studies in the putative area of its distribution. The present IUCN conservation status is preliminarily estimated as “Data Deficient” (DD). 

Studied specimens (paratypes). S Vietnam, Dak Lak Province, Buon Don District, Yok Don National Park, open dry dipterocarp forest and woodland, terrestrial ephemeroid tuberiferous herb with prostrate green or dark green leaves in open grassy place, at elevation of 200–300 m a.s.l., locally abundant, 10 October 2017, N.V. Canh, AL 316 (LE LE01074054, http://en.herbariumle.ru/?t=occ&id=19021). Yok Don National Park, open dry dipterocarp forest, 3 June 2018, Nguyen Van Canh s.n. (photos – LE LE01087398, http://en.herbariumle.ru/?t=occ&id=38797). Yok Don National Park, open dry dipterocarp forest, 30 August 2018, Nguyen Van Canh s.n. (photos – LE LE01087397, http://en.herbariumle.ru/?t=occ&id=38796) and Dinh Quang Diep, s.n. (photos – LE LE01087292, http://en.herbariumle.ru/?t=occ&id=19014). Yok Don National Park, open dry dipterocarp forest and woodland with dense low bamboo, at an elevation of 200–300 m a.s.l., terrestrial ephemeroid tuberiferous herb with prostrate leaves in open wet place, very rare, found in one location, 24 October 2019, L. Averyanov, Nguyen Van Canh, T. Maisak, AL 1167 (LE LE01066622, http://en.herbariumle.ru/?t=occ&id=12390). 

ACKNOWLEDGMENTS 

The studies were supported in parts by the Russian Foundation for Basic Research, projects 19-54-54007 & 20-04- 00339, and the institutional research project of the Komarov Botanical Institute of the Russian Academy of Sciences “The Vascular Plants of Eurasia: the systematics, flora and plant resources” (АААА-А19-119031290052-1). We thank Mr. Cong Van Vo for access to his private orchid collection and photos of Dendrobium praecinctum, Dr. Pankaj Kumar for his kind help in plant identification and Prof. D.D. Sokoloff for his ideas on the morphology of the flower of Apetalanthe. 

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