Dendrobium vietii Aver. & V.C.Nguyen

Averyanov, Leonid V., Nguyen, Van Canh, Vuong, Truong Ba, Nuraliev, Maxim S., Nguyen, Khang Sinh, Maisak, Tatiana V., Yudova, Daria A., Saidov, Nikita T., Nguyen, Cuong Huu & Nong, Duy Van, 2024, New orchids in the flora of Vietnam VIII (Orchidaceae: Epidendroideae, tribes Malaxideae, Neottieae and Podochileae), Phytotaxa 658 (1), pp. 1-49 : 24-26

Dendrobium vietii Aver. & V.C.Nguyen , sp. nov.

( Fig. 11 )

Diagnosis: —The new species is morphologically close to D. aphyllum , differing from the latter in uniformly pink sepals and petals with somewhat thick texture, oblong broadly lanceolate sepals shorter than 2.6 cm and wider than 6.5 mm, narrowly ovate petals 1–1.4 mm wide, ciliate petal margin, lip with 2 large reddish purple areas aside of the disk, and column incompletely enveloped by lip side lobes.

Type: — VIETNAM. Dak Lak Province: Krong Ana District, Buon Trap Townlet, dry evergreen forest at elevation of 550–600 m a.s.l., wild collected plant cultivated by Mr. Bui Quoc Viet in 2015, flowers light pink-violet, lip disk with reddish-purple veins, type prepared on 30 April 2015, L. Averyanov, T. Maisak, AL 047 (holotype LE LE 01059883! https://en.herbariumle.ru/?t=occ&id=11935, photos of plant used for preparation of type herbarium specimen LE LE 01088450 https://en.herbariumle.ru/?t=occ&id=47173).

Etymology: —The species is named after its discoverer, Mr. Bui Quoc Viet.

Description:—Epiphytic herb with few suberect or pendulous stems densely clustering on rhizome. Rhizome plagiotropic, short, glabrous, bearing numerous wiry, gray to light yellowish roots. Stem fleshy, to 20 cm long, 5–7 mm in diameter, glabrous; young stems leafy throughout; old stems leafless, naked near the base, olive green, in apical half covered by white, papyraceous, overlapping, dry leaf sheaths. Leaves sub-distichous, sessile, green, sometimes with light purple tint, glabrous, sheathed at the base; sheaths tubular, pale green, speckled with purple; leaf blade oblong broadly lanceolate, (3.5)4–5(6) cm long, (0.8)1–1.2(1.4) cm wide, obtuse to acute, conduplicate with prominent median vein. Inflorescence arising from nodes of leafless stem, with 1(2) flowers; peduncle dull purple, 3–5 mm long, glabrous; floral bracts whitish, scarious, triangular, acute, 2–3 mm long, glabrous. Pedicel and ovary not resupinate, terete, almost straight, dull to light purple, (2)2.2–2.6(2.8) cm long, about 1.5 mm in diameter, glabrous. Flowers widely opening, of somewhat thick texture; sepals and petals uniformly light pink, acute to shortly apiculate; lip light pink with purple secondary veins at base and two large dull reddish-purple areas aside of the disk. Sepals oblong broadly lanceolate, (2.2)2.4–2.5(2.6) cm long, (6.5)7–9(9.5) mm wide, with entire (not ciliate) margin, glabrous; lateral sepals slightly oblique at base. Petals narrowly ovate, (2)2.1–2.3(2.4) cm long, (1)1.1–1.3(1.4) cm wide, ciliate along margin, otherwise glabrous. Lip almost orbicular (when flattened), (2.1)2.2–2.4(2.5) cm in diameter, at base attenuate into short narrow rectangular claw 2.4–2.6 mm long, 1.5–1.6 mm wide, ciliate along margin and shortly white hairy on both surfaces. Column erect, stout, white with few small purple marks, 3.8–4.2 mm tall, 2.5–2.7 mm wide, glabrous; anther cap helmet-shaped, white, finely papillose, 2.4–2.5 mm tall, 2–2.2 mm wide, truncate and slightly emarginate at apex; column foot almost straight, 4.7–4.9 mm long. Fruits unknown.

Habitat and phenology: —Clustering epiphyte. Primary and secondary dry evergreen forests at elevations of 550–600 m a.s.l. Very rare. Flowers in April–May (under cultivation).

Distribution: —Endemic to S Vietnam: Dak Lak Province (Krong Ana District).

Conservation status: —Due to the scarcity of the available information on the single known population of Dendrobium vietii we estimate the conservation status of this species as Data Deficient (DD). Comprehensive field studies are needed for its clarification.

Notes: — Dendrobium vietii is morphologically most close to D. aphyllum ( Roxburgh 1795: 34) Fischer (1928: 1416 , see also Bose & Bhattacharjee 1980, Seidenfaden 1985, Seidenfaden & Wood 1992, Chen et al. 1999, Raskoti 2009), from which it differs in sepals and petals with somewhat thick texture, uniformly pink (vs. sepals and petals very thin, almost transparent, mauve, pure white or white with purple tint), sepals oblong broadly lanceolate, shorter than 2.6 cm and broader than 6.5 mm (vs. sepals lanceolate, oblong lanceolate or narrowly lanceolate, often longer than 2.6 cm and narrower than 5 mm), petals narrowly ovate, 1–1.4 cm wide, ciliate along margin (vs. petals broadly lanceolate or elliptic-oblong, often less than 1 cm wide, with entire or finely erose margin), lip with 2 large reddish-purple areas aside of the disk (vs. center of lip white or white with yellowish tint, without reddish areas or only with purple veins), column not prominently enveloped by the basal sides of the lip (vs. the basal sides of the lip overlapping, completely enveloping the column).

According to our observations, D. vietii is an extremely rare species. To our opinion, it may represent a natural hybrid between the very common and widespread D. aphyllum and any closely related species with a somewhat thick texture of sepals and petals and a lip bearing two purple spots in the center. Dendrobium vietii surely resembles morphologically two species belonging to this group: D. anosmum Lindley (1845: 32 , see also Seidenfaden 1985, Seidenfaden & Wood 1992, Comber 2001, Wood 2014) and particularly D. parishii Low (1863: 281 , see also Bose & Bhattacharjee 1980, Seidenfaden 1985, Chen et al. 2009). Both of them are common in Vietnam, and one of them can possibly be the second parent of such a natural hybrid.

Figures

FIGURE 11. Dendrobium vietii. A. Flowering plant. B. Plant with young leafy shoot. C. Flowering leafless shoot. D, E. Portions of flowering leafless shoot. F. Flower, front view. G, H. Flowers, half-side view. I. Flower, side view. J. Column and central portion of lip, front view. Photos by L. Averyanov from living plant prior to the preparation of the type herbarium specimen L. Averyanov, T. Maisak, AL047. Photo correction and design by L. Averyanov and T. Maisak.