Dendrobium namdongense Aver. & C. H. Nguyen 2024, sp. nov.
Creators: name: Nguyen, Cuong Huu
name: Dang, Ha Van
name: Nguyen, Yen Thi
name: Nguyen, Ly Van
name: Averyanov, Leonid V.
name: Maisak, Tatiana V.
name: Shvanova, Valeria V.
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Plantae
Tracheophyta
Liliopsida
Asparagales
Orchidaceae
Dendrobium
Dendrobium namdongense

description: Dendrobium namdongense Aver. & C.H.Nguyen, sp. nov. (Fig. 1)
Type:— VIETNAM. Thanh Hoa Province: Quan Hoa District, Nam Dong Community, the territory of Nam Dong Conservation Area, primary broad-leaved evergreen and mixed (with Pinus kwangtungensis) humid forest on very steep rocky slopes on solid, marble-like highly eroded limestone at elevation 900–1100 m a.s.l. on steep rocky slope, clustering appressed epiphyte on mossy trees on rocky mountain top, flowers tepals white to light yellowish or pinkish with purple veins, lip dark purple, rare, 4 May 2024, Nguyen Huu Cuong, Nguyen Van Ly, L. Averyanov, T. Maisak, AL 3075 (holotype VNF NHC 20240506001, isotypes LE LE 01276172 & LE LE 01276518, photos of plants used for preparation of the type specimens LE LE 01125079 https://en.herbariumle.ru/?t=occ&id=226271, LE LE 01255109 https://en.herbariumle.ru/?t=occ&id=226270).
Etymology:— The species epithet refers to the Nam Dong Conservation Area, where this plant was discovered.
Diagnosis:— The new species differs from most similar Dendrobium fuscifaucium and D. hekouense in distinctly smaller pseudobulbs, 5–9 mm tall; leaves, 6–13 mm long with very short peduncle, less than 1 mm long; sepals and petals with distinct purple veins; short lip, 11.5–14.5 mm long, lip side lobes papillulate, obliquely semicircular, lip median lobe semicircular, 4.5–6.5 mm wide, lip disc flat or with two low insignificant keels; anther cap rectangular, semiglobular at apex, and time of flowering during April–May.
Description:— Miniature epiphytic glabrous herb with many distichous pseudobulbs densely clustering on thin, creeping plagiotropic rhizome. Pseudobulbs brown to brown purple, 1–2-leaved, closely touching each other, narrowly ovate to broadly fusiform or ellipsoid, (5)6–8(9) mm tall, (2.5)3–4(4.5) mm in diameter, shortly stalked, consisting of 2(3) internodes, each (1.5)2–3(4) mm long, bladeless sheaths, pale green to scarious, with longitudinal nerves, soon weathered into papyraceous or fibrous remnants. Leaves subsessile; petiole sheathed, white, scarious, 0.8–1 mm long; leaf lamina narrowly ovate to broadly elliptic, dull green, often flushed with purple toward the apex and along the margin, coriaceous, conduplicate, (6)9–12(13) mm long, (3.5)4–5(5.5) mm wide, blunt to rounded at base and apex. Inflorescences 1–2 on individual pseudobulb, subterminal, arising from the apex of leafless pseudobulbs, 1- flowered; peduncle less than 1 mm long, with 1 very small, insignificant, tubular sheath at base; floral bract triangular ovate, funnel-shaped, acute, (2.5)3–3.5(4) mm long, white to light gray, scarious; pedicel and ovary slightly curved, (4.5)5–6.5(7) mm long, 0.8–1 mm in diameter, white to white tinged with purple. Flowers spreading horizontally, widely opening; sepals and petals white, sometimes with a light yellow or pink tint, with purple veins on both sides; the lip dark purple inside, white with a purple tint outside; side lobes white to light yellowish; the median lobe dark purple on both sides, disc and medial lobe adaxially with dense whitish hairs. Median sepal oblong narrowly ovate, (6)6.5–7.5(8) mm long, 4–4.5 mm wide, obtuse, with 3 purple veins. Lateral sepals obliquely broadly triangular, (7)7.5–8(8.5) mm long, (10.5)11–12(12.5) mm wide at the base, acute, with 5 purple veins; mentum saccate, (9)10(11) mm long, 5.5–6 mm wide, slightly incurved, apically round, and slightly bilobed. Petals oblong narrowly obovate, (6)6.5–7(7.5) mm long, (3.2)3.5–4(4.2) mm wide, obtuse, with 1 violet vein. Lip trilobed, recurved, with erect side lobes, and strongly recurved median lobe, broadly obdeltoid (when flattened), (11.5)12–14(14.5) mm long and wide; side lobes erect, obliquely semicircular, 3.5–4 mm long, 6–7 mm wide at the base, finely ciliate along the margin; median lobe, semicircular, entire or obscurely emarginate, (2.5)3(3.5) mm long, (4.5)5–6(6.5) mm wide, margin ciliate; disc and surface of median lobe adaxially densely pubescent with long hairs, often branching at apex, disc and base of median lobe almost flat or with two low, hardly visible longitudinal keels. Column 2.5–3 mm tall, 3–3.5 mm wide, finely papillulate on sides, stigma concave, semicircular, about 1.5 mm in diameter; column foot 9–9.5 mm long, 5–5.5 mm wide in broadest part, white proximally, dark purple in distal half, glabrous, almost round at apex. Anther cap rectangular helmet-shaped, about 1.8 mm tall, 2 mm wide, at front view almost semiglobular at apex, light green, front margin white, finely papillulate; pollinia 4, bright yellow, narrowly conoid, slightly curved, 1.1–1.2 mm long. Capsules (not ripe) dark green, narrowly obconoid, longitudinally ribbed, 10–12 mm long, 3.5–4.5 mm in diameter, glabrous.
Distribution:— Thanh Hoa Province, Quan Hoa District, endemic to limestone area of Nam Dong Conservation Area.
Ecology and habitat: —Miniature creeping epiphyte with densely clustering appressed pseudobulbs; often observed on mossy trees in primary broad-leaved evergreen and mixed (with Pinus kwangtungensis) humid forest on tops of remnant karstic mountains composed with solid, marble-like highly eroded limestone at elevations of 900–1100 m a.s.l. The climate in the area where Dendrobium namdongense was found is recognized as a tropical monsoon with a hot and humid summer, and dry and cool winter periods (Nguyen Khanh Van et al. 2000). The summer rain season lasts from May until September, with daily usual temperatures between 23–38ºC (with a recorded maximum 41ºC). The dry winter season lasts from September to April, with usual temperatures between 26–23ºC (with a recorded minimum 6ºC). Annual rainfall averages nearly 1050 mm. Cloudy fogs and mists on top of limestone mountains harboring habitats of D. namdongense are very common all year.
Phenology: —Flowers between April–May (onset of rainy season).
Notes: —The new species described here belongs to the group of miniature species from Dendrobium section Dendrobium, including D. fuscifaucium Souvann. & Kumar in Souvannakhoummane et al. (2022), D. hekouense Z.J.Liu & L.J.Chen in Liu & Chen (2011), D. luoi L.J.Chen & W.H.Rao in Deng et al. (2016), and D. wangliangii Hu, Long & Jin (2008). These species share remarkable characters such as an appressed, subtitle epiphytic habit, small stature of vegetative parts, short 1-flowered inflorescence, and comparatively larger flowers appearing on leafless pseudobulbs. Among these species, D. namdongense is morphologically most similar to D. fuscifaucium, which originated supposedly from Laos (Souvannakhoummane et al. 2022), and D. hekouense, recorded from southern China and northern Vietnam (Liu & Chen 2011, Zhou et al. 2016, Averyanov et al. 2018, Cribb et al. 2021). Our newly described species can be differentiated from both these species by its distinctly smaller pseudobulbs, 5–9 mm tall (vs. 8–14 mm) and leaves, 6–13 mm long (vs. 20–52 mm), very short peduncle, less than 1 mm long (vs. 1–4.5 mm), sepals and petals with distinct purple veins (vs. purple veins absent, or hardly visible), median sepal oblong narrowly ovate (vs. median sepal ovate to broadly ovate), shorter lip, 11.5–14.5 mm long (vs. lip 14–20 mm), lip side lobes papillulate, obliquely semicircular (vs. side lobes fimbriate, obliquely triangular), lip median lobe semicircular, 4.5–6.5 mm wide (vs. median lobe reniform, 7–10 mm wide), lip disc almost flat or with two low, hardly visible keels (vs. disk with two distinct prominent keels), hairs on the lip simple and branching (vs. hairs simple), and anther cap rectangular, semiglobular at apex (vs. anther cap conoid). The discriminative morphological characters of the mentioned species are presented in Table 3.
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Conservation: —According to the available data, Dendrobium namdongense is an extremely rare orchid. Until now, only one tiny wild population with an extent of occurrence (EOO) and an area of occupancy (AOO) less than 100 km ² and 10 km ² respectively, has been confirmed. According to our field observation, the population likely includes less than 50 colonies, almost all of which are of flowering maturity. The species is speculated to have ornamental value and thus highly desired in the unofficial wild plant market. It is possible that the species can quickly turn extinct in the wild due to overcollection due to poaching and illegal trade. According to the IUCN Red List (2024) criteria, we establish its status as Critically Endangered, CR A3(d); B1ab(i–v)+2ab(i-v); C1a(i–ii)+2(i–ii); D1.
description: Published as part of Nguyen, Cuong Huu, Dang, Ha Van, Nguyen, Yen Thi, Nguyen, Ly Van, Averyanov, Leonid V., Maisak, Tatiana V. & Shvanova, Valeria V., 2024, Dendrobium namdongense (D. sect. Dendrobium), a new miniature orchid from limestone mountains of northern Vietnam, pp. 200-206 in Phytotaxa 664 (3) on pages 201-205, DOI: 10.11646/phytotaxa.664.3.5, http://zenodo.org/record/14517360