Hemipilia uniflora Aver., B.H.

Averyanov, Leonid V., Nguyen, Van Canh, Vuong, Truong Ba, Quang, Bui Hong, Nguyen, Khang Sinh, Le, Tuan Anh, Binh, Tran Duc, Maisak, Tatiana V. & Nguyen, Cuong Huu, 2025, New orchids in the flora of Vietnam X (Orchidaceae, Orchidoideae, tribe Orchideae, Epidendroideae, tribes Gastrodieae, Arethuseae, Cymbidieae, and Vandeae), Phytotaxa 681 (1), pp. 20-54 : 22-24

Hemipilia uniflora Aver., B.H. Quang & K.S.Nguyen, sp. nov.

( Fig. 1 )

Diagnosis: — Hemipilia uniflora differs from its congeners in inflorescence bearing predominantly 1 flower, peduncle and ovary densely papillose pubescent, and lip deeply dissected into 3 obtriangular lobes dentate at truncate apex.

Type: — VIETNAM. Ha Giang Province: Quan Ba District, Bat Dai Son Nature Reserve, Thanh Van Commune, Mo Sai Village, around point 23º07ʹ46.4ʺN 104º57ʹ56.2ʺE, at elevation of 1000–1190 m a.s.l., karstic, highly eroded mountains composed of solid marble-like limestone, primary evergreen broad-leaved and mixed (with Pseudotsuga sinensis ) humid forest on steep rocky slopes near mountain tops, miniature terrestrial tuberiferous herb, 3 April 2024, Bui Hong Quang, Nguyen The Cuong, Khang Sinh Nguyen, Tran Duc Binh, BHQ1019 (holotype HN, isotype LE: LE 01277493 https://en.herbariumle.ru/?t=occ&id=248283, photos of plants used for preparation of the type specimen LE: LE 01255154 https://en.herbariumle.ru/?t=occ&id=228656, LE 01255208 https:// en.herbariumle.ru/?t=occ&id=241360).

Description:—Herb miniature, terrestrial, tuberiferous, rootless, glabrous. Tuber underground sub-globular, ovoid, or shortly cylindrical, pale yellowish to light brownish, (4)5–8(9) mm long, densely covered with soft white root hairs; tuber of the next generation developing at the base of stem. Stem arising from tuber, oblique to erect, (2.8)3–5(5.5) cm tall, terete, (0.8–)1(–1.2) mm in diameter, white at base, light pink to light greenish, finely speckled with dull purple, at base with 1–2(3) tubular, white or light greenish acute bracts (3)3.5–8(10) mm long and 1.2–1.4 mm wide (when flattened) and 1 horizontally recurved cauline leaf. Leaf sessile, broadly lanceolate to narrowly ovate, often slightly falcate, conduplicate, adaxially rich green, abaxially light greenish to almost white, heavily speckled with brownish purple on both sides, (1.4)1.6–2.6(3) cm long, (5)6–10(11) mm wide, tapering from wide base to acute apex, with prominent median vein. Inflorescence predominantly uniflorous, rarely spike-like with 2 flowers; peduncle ebracteate, light pink to greenish, finely speckled with dull purple, (1.8)2–3(3.2) cm long densely papillose pubescent. Floral bracts erect, triangular, light greenish, (1.5)2–3(3.5) mm long, (0.6)0.8–1.2(1.4) mm wide, tapering from broad base to acute apex. Ovary terete, erect, somewhat curved, longitudinally ribbed, greenish, tinged with brownish purple, 8–9 mm long, 0.6–0.8 mm in diameter, densely papillose pubescent. Flowers usually solitary, rarely two, distant on 1.5–2(3) mm, sessile, resupinate, widely opening, pink to light purple with purple spots on lip center, (4.6)5(5.4) mm across. Median sepal erect, 1-veined, rectangular oblong, cymbiform, (3.8)4(4.2) mm long, (1.8)2(2.2) mm wide (when flattened), obscurely truncate and cucullate at apex, forming with petals hood, embracing column from above. Lateral sepals reflexed or recurved, straight, 1-veined, obliquely oblong narrowly ovate, (4.6)5(5.4) mm long, (1.8)2(2.2) mm wide, obtuse to truncate at apex. Petals forward directed, without distinct veins, obliquely obovate, narrowing to the base, slightly concave, (2.8)3(3.2) mm long, (2.4)2.5(2.6) mm wide, round at apex. Lip downwards directed, spurred, deltoid in outline, without ornamentation, almost flat, finely papillulate, (8)8.5–9(9.5) mm long, (9.5)10–10.5(11) mm wide, deeply dissected to 3 lobes; lobes subequal, obtriangular, 4.5–5 mm long, (1.8)2(2.2) mm wide proximally, distally broadening to (3.8)4(4.2) mm wide, truncate and irregularly dentate at apex; spur at broad angle to lip, down directed, straight, narrowly clavate, obtuse and slightly dorsi-ventrally flattened at apex, as long or little shorter as ovary, 7–8 mm long, about 0.4 mm in diameter at the base, broadening to 1.6–1.8 mm wide at apex. Column erect, stout, obscurely half-globular, 1–1.2 mm tall and wide; anther erect, with 2 separate, close, parallel thecae narrowing (but not extending) at base and embracing caudicles; viscidia 2, separate, naked or covered by individual early agglutinated bursicle; rostellum in form of small, insignificant fold placed at the base of anther between viscidia; auricles small, finely verruculose; stigma entire, slightly concave placed below rostellum, facing to almost circular spur entrance. Pollinaria 2, very small, clavate, with short caudicle and almost circular viscidium. Fruits not seen.

Etymology: —The species name refers predominantly uniflorous inflorescence.

Ecology and phenology: —Primary evergreen broad-leaved and mixed (with Pseudotsuga sinensis ) humid forest on highly eroded, solid marble-like limestone at elevation of 1000–1200 m a.s.l., commonly on steep rocky slopes near mountain tops. Flowers in February–April.

Distribution: — VIETNAM (Ha Giang Province, Quan Ba district, Bat Dai Son Nature Reserve). Endemic of Bat Dai Son Mountains.

Conservation status: — Hemipilia uniflora is known from a single location with an Area of Occupancy (AOO) of less than 10 km 2. Owing to extensive selected logging in this area which is inferred as continuing decline of habitat, this species is assessed globally as Critically Endangered [CR B2ab(iii)] following the formal criteria proposed by the IUCN (2024).

Notes: —Curiously our discovered plant fits in a series of morphological characters with recently segregated genus Sirindhornia H.A.Pedersen & Suksathan ( Pedersen et al. 2003: 393) distributed in E Myanmar (Shan State), SW China (Yunnan), and NW Thailand (Tak & Chiang Mai provinces). Like three known species of Sirindhornia , our plant has stem and ovary densely papillose pubescent, one prostrate leaf heavily speckled with brownish purple spots, minute scarious floral bracts much shorter than ovary, sessile resupinate pink flowers, spurred 3-lobed lip, small, hardly visible, fold-like rostellum placed between close thecae having no extensions, entire concave stigma, and 2 clavate separate pollinia. It is remarkable that the column structure of our plant looks almost identical with those figured on the Kerr hand drawing on the herbarium sheet Kerr 474 (K K000595756) of the paratype of the type species of the genus. These drawings are dramatically different from figures illustrated the genus protologue ( Pedersen et al. 2003, fig. 396, fig. 3) repeated later in the genus assessment ( Pedersen et al. 2014: 263, fig. 154). Actually, our discovered plant together with all recognized species of Sirindhornia is surely very close to the genus Chusua Nevski (1935: 670) , Orchis Linne (1753: 939) , Ponerorchis Reichenbach (1852: 227) , and Tsaiorchis Tang & Wang (1936: 131) in all basic morphological characters. In this connection, the segregation of Sirindhornia remains very questionable. Two other closest allies, Hemipilia Lindley (1835: 296) and Amitostigma Schlechter (1919: 91) differs from Sirindhornia , Chusua , Orchis , Ponerorchis , and Tsaiorchis alliance in the broad prominent rostellum ( Hemipilia ) and in very short pollinarium caudicles with naked separate viscidia ( Amitostigma ). It may be noted that the more or less acceptable morphological delimitation of mentioned genera s. str. does not entirely fit with clades identified by molecular cladistics ( Tang et al. 2015, Jin et al. 2017) tentatively applied to the alliance taxonomy. In fact, according to its morphology Hemipilia uniflora shows unclear generic position between Sirindhornia , Hemipilia , and Ponerorchis having such characters as papillose hairy peduncle and ovary (typical for Sirindhornia ), one leaf speckled with purple (common in Hemipilia ), and parallel thecae, closely allied each other with very narrow connective (usual in Ponerorchis ). Further molecular study of our plant may bring evidence that Sirindhornia clade based on study of a single species, Sirindhornia pulchella H.A.Pedersen & Indham. in Pedersen et al. (2003: 398), does not form too isolated clade, sister to the clade formed by Ponerorchis , Hemipilia and related genera ( Jin et al. 2014, 2017, Tang et al. 2015). Meanwhile, our discovered plant before more detailed studies may be tentatively regarded as a member of the genus Hemipilia sensu lato.

Figures

FIGURE 1. Hemipilia uniflora. A, B. Flowering plants in natural habitat. C, D. Flattened flowering plants prepared for herbarization. E. Leaf, adaxial and abaxial side. F. Inflorescence. G, H. Intact flower, front (G) and half-side view (H). I. Flattened flower, front view. J. Flower, view from above. K. Flower, with median sepal and petals removed. L. Flower, view from rear. M. Flower view from below. N. Median sepal, adaxial side. O. Petals, adaxial and abaxial side. P. Anther, view from above. Photos by Khang Sinh Nguyen, from plants used for preparation of the type specimens BHQ1019. Photo correction and design by L. Averyanov and T. Maisak.