Gastrochilus nanus Z.H.Tsi

Averyanov, Leonid V., Thai, Tran Huy, Nguyen, Van Canh, Truong, Ba Vuong, Maisak, Tatiana V., Doan, Nga Thi & Nguyen, Khang Sinh, 2022, New orchids in the flora of Vietnam (Orchidaceae, Aeridinae), Phytotaxa 572 (1), pp. 43-60 : 48-52

Gastrochilus nanus Z.H.Tsi in Boufford et al. (1990: 121), Chen et al. (2009: 496), Zhou et al. (2016: 62).

Type:— CHINA. China, Guizhou Province, Jiankou Xian, Yuao , in the valley of the Haiwan River, elevation ca. 1000 m, 26 August 1986, Sino-Amer. Guizhou Bot. Exped. 407 (holotype PE?, isotypes A 00271832, HGAS?) .

( Fig. 5 )

Description:— Herb monopodial perennial epiphytic. Stems creeping or pendulous, (3)4–7(8) cm long, leafy and rooting throughout, with internodes 5–6 mm long. Leaves numerous, densely spaced, distichous, sessile; leaf blade adaxially dark green with unclear dirty purple marks, abaxially pale green, narrowly elliptic, (0.8) 1.2–1.6 mm long, (4.5)5–5.5(6) mm wide, aristate, with apical seta 1.2–1.5 mm long and often with two small rudimentary lateral dents. Inflorescences axillary, placed throughout stem, subumbellate, 3–6-flowered; peduncle horizontal, (4)5–7(8) mm, upper part slightly inflated, with 1 or 2 tubular bracts at base; floral bracts light green, triangular, acute, 1–1.2 mm; pedicel and ovary 5–6 mm long. Flowers yellowish green, sepals and petals with dull purple median stripe, lip white with bright yellow center, spoor greenish. Sepals and petals narrowly ovate, concave, blunt to obtuse, 2.5–3 mm long, lateral sepals and petals slightly oblique. Lip spurred, entire, reniform, (3)3.2(3.4) mm long, (3.8)4(4.2) mm wide, with thin entire or obscurely crenulate margin, round at apex, at center with cushion, adaxial surface and margin hairy with white stiff hairs, which longer and more dense at spur entrance; spur shortly cylindrical, slightly down curved, nearly parallel to ovary, 3.5–4 mm long, 1.8–2 mm in diameter, slightly inflated at rounded apex. Column 0.8–1 mm tall; anther cap hemispheric, 0.2–0.3 mm in diameter, with small beak at front. Fruits unknown.

Ecology and phenology:—Canopy epiphyte on mossy branches of tall trees. Primary humid evergreen broadleaved and coniferous montane forests (with Pinus , Fokienia , and Tsuga ) on rocky karstic limestone at elevations of 1400–1600 m a.s.l. Flowers in June–July (August).

Distribution:— Vietnam (Cao Bang Province, Bao Lac District). S China (Guizhou, Jiangxi).

Conservation status:—Up to now, the species is known in Vietnam only from the one location where it forms a population with few mature individuals in the area influenced by wide deforestation. Its conservation status is tentatively assessed here as a nationally Critically Endangered CR (B1a,b(i-v); C2a(i); D).

Notes:— The location of the species discovered in northern Vietnam extends the known species area from populations known in central China ( Kong 2011, Zhou et al. 2016) on more than 500 km in the SE direction. Vietnamese plant differs from the type in stem to 8 cm long with internodes 5–6 mm long (vs. stem 3–4 cm long, leaves closely arranged, with internodes 1.5–2.5 mm long), leaves setose with seta 1–2 mm long (vs. leaves acute without distinct setae), and epichile rounded at apex (vs. epichile notched at apex). It may be represent a new variety, which better understanding needs more studies.

Studied specimens:— VIETNAM, herbarium specimen prepared from living plant on 01July 2022 by L. Averyanov , T. Maisak, CPC 7581 TM 1184 (flowers odorless, sepals and petals pale yellowish with greenish base, lip with olive yellow fleshy center and thin white margin, hypochile side-lobes pale yellow with unclear purple marks, column white, anther cap yellowish) collected in Cao Bang Province, Bao Lac District, Hong An Municipality, Mi Lung Village, primary broad-leaved and mixed humid evergreen forest (with Podocarpus , Pinus , Fokienia and Tsuga ) on very steep slopes and along rocky ridge composed with solid crystalline highly eroded limestone at elevation about 1500–1550 m a.s.l. around point 22°49’15.4’’N 105°49’53’’E, canopy epiphyte on mossy tree on shady, humid slope, rare, 21 November 2014, L. Averyanov , N.T. Hiep, N.S. Khang, T. Maisak, L. Osinovetz (LE01168963 https://en.herbariumle. ru/?t=occ&id=140412, analytical photos LE01123337 https://en.herbariumle.ru/?t=occ&id=137124).

Figures

FIGURE 5. Gastrochilus nanus Z.H.Tsi.A. Flowering plant, view from above and from below. B. Flowering portion of shoot. C. Intact inflorescence, frontal view. D. Intact inflorescence, side view. E. Intact flowers, frontal view. F. Pedicel, ovary, and intact flower, frontal view, side view, and view from behind. G. Flattened flowers without lip, with anther cap and with anther cap removed. H. Lip, frontal view. I. Lip, view from below and half-side from below. J. Lip sagittal section. All photos made by L. Averyanov from L.Averyanov, T. Maisak, CPC 7581 TM 1184; correction and plate design by L. Averyanov and T. Maisak.