Cleisostoma aspersum (Rchb.f.) Garay (1972: 169)

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 : 44-47

Cleisostoma aspersum (Rchb.f.) Garay (1972: 169) ; Seidenfaden (1975: 12, fig. 2); Pearce, Cribb (2002: 508); Wang et al. (2015: 283).

( Figs. 1 , 2 )

≡ Sarcanthus aspersus Reichenbach (1865: 297) . Type : — MYANMAR. Burma , Moulmein, Veitch 39 (holotype W herbarium number 53509) .

= Cleisostoma aspersum auct. non Garay: Seidenfaden (1992: 387); Averyanov (1994: 378); Averyanov, Averyanova (2003a: 21).

Description:—Herb perennial monopodial epiphytic. Stem simple or basally few branched, semi-woody, erect or ascending, 1–3 cm long, slightly flattened, covered throughout by leaf sheaths, with 2–3(4) leaves, at base with few wiry, flexuose white roots; internodes 0.5–1 cm long. Leaves subdistichous, sessile, dorsiventral, leathery, straight or slightly recurved or twisted, oblong, (9)10–12(13) cm long, (2.2)2.5–3(3.2) cm wide, truncate, unequally shortly (3)4(5) toothed at apex. Inflorescence lateral raceme, (12)16–18(20) cm long, scape and rachis dirty purple violet; scape 3–4 cm long, horizontal or slightly pendulous; rachis (10)12–14(16) cm long, straight to slightly zig-zag, with (10)14–18(20) spirally arranged, lax flowers distant on (5)7–9(11) mm. Floral bracts dark dirty violet to almost black, minute, triangular, obtuse, 1–1.2 mm long, about 1 mm wide. Pedicel and ovary terete, longitudinally grooved, (7)8–9(10) mm long, (0.9)1(1.1) mm in diameter, glabrous, pale green with dull purple tint, slightly broadening at the base. Flowers widely opening, (7.5)8–9(10.5) mm across; sepals and petals somewhat fleshy, glabrous, spreading, pale yellow, with pale purple median vein outside; lip white, with yellow back wall callus; column white; anther cap white with purple longitudinal stripe; pollinia pale yellow. Sepals narrowly obovate, concave, blunt to rounded at apex, (3.8)4–4.5(4.8) mm long, (2)2.2–2.4(2.6) mm wide; median sepal slightly cucullate; lateral sepals somewhat oblique. Petals narrowly obovate, blunt to obtuse at apex, (3.4)3.6–3.8(4) mm long, (1.6)1.7–1.9(2) mm wide, slightly oblique. Lip spurred, (5.4)5.6–5.8(6) mm long (from spur apex to the apex of epichile), 3-lobed; side-lobes thin, erect, rectangular, truncate, 1–1.2 mm long, 1.8–2 mm wide, shallowly bilobed; median lobe fleshy, triangular, concave, upright ascending, slightly inflated at the base, shallowly emarginate at apex, (0.8)0.9(1) mm long and wide; spur shortly cylindrical bent at middle, almost perpendicular to ovary, (2.3)2.4–2.6(2.8) mm long, (0.9)1(1.1) mm in diameter, round at apex, without longitudinal septum inside. Back-wall callus simple, glabrous, longitudinally rectangular at front, almost triangular in sagittal section, 1–1.2 mm long, 0.5–0.6 mm wide, and 0.8–0.9 mm tall, allied by its apical pat to slightly inflated front wall. Column short, broad, indistinctly cubic, 1–1.2 mm tall and wide, at front with small rostellum supporting small viscidium; stigma in form of transversely oblong hollow. Anther cap helmet shaped, 1 mm tall and wide, 1.2–1.4 mm long, with prominent triangular beak. Pollinia 2, each incompletely split into 2 half-globular bodies. Stipe (tegula) in form of narrowly lanceolate to almost filiform scarious stalk 0.8–1 mm long; viscidium in form of small disk 0.1–0.2 mm in diameter, slightly bent abaxially. Fruits unknown.

Ecology and phenology:—Epiphyte on tall mossy trees. Primary evergreen broad-leaved very humid forest on stratified highly eroded limestone at elevation 1000–1100 m a.s.l. Flowers in May–June.

Distribution:— Vietnam (Ha Giang Province, Quan Ba District). Bhutan, NE India, SW China (Yunnan).

Conservation status:—Preliminarily estimated as nationally critically endangered, CR (B1a,b(i-iii,v), B2a,b(iiii,v); D). Available observations indicate that the species in Vietnam meets the following IUCN Red List Categories and Criteria ( IUCN 2019) as following: only two populations were discovered with extent of occurrence (EOO) less than 100 km 2 (B1a) and the area of occupancy (AOO) less than 10 km 2 in two known locations (B2a); observed in both cases the expected continuing of decline (b) of extent of occurrence (i), area of occupancy (ii), area, extent and quality of habitat (iii), number of mature individuals (v); populations are very small with estimated number of mature individuals less than 50 (D).

Notes:—All early reports of this species in Vietnam were doubtful ( Seidenfaden 1992, Averyanov 1994, Averyanov & Averyanova 2003a) and later were identified as a new species, Cleisostoma melanorachis Averyanov & Averyanova (2006a , b). The present report represents actually the first verified record of this species in Vietnam based on observations in nature and collected voucher herbarium specimens. Respectively, we provide here the description and illustrations for this rare species assessed in Vietnam as Critically Endangered.

In floral morphology, Cleisostoma aspersum resembles described earlier C. flavescens Averyanov & Averyanova (2003b) , but well differs in shorter stems less than 3 cm (vs. stem longer than 3 cm), leaves 8–13 cm long, truncate, 4–5 denticulate at apex (leaves 12–20 cm long, bilobulate at apex with roundish lobes), simple inflorescence (vs. inflorescence paniculate, many branching), lip side-lobes shallowly bilobulate, flat (vs. lip side-lobes entire, flabellate, finely crisped along the margins). Cleoisostoma aspersum also resembles C. discolor Lindley (1845: 59) , but well differs in twice smaller flowers, fleshy lip (vs. lip thin textured), entire or slightly crenulate lip margin (vs. lip margin erose to irregular denticulate), side-lobes erect, rectangular, shallowly bilobed (vs. side-lobes recurved, entire, broadly flabellate), and median lobe fleshy, broadly triangular, upright ascending (vs. median lobe thin, oblong triangular, recurved).

Studied specimens:— VIETNAM, herbarium specimen prepared from cultivated plant in 20.06.2022, by L. Averyanov , T. Maisak, VR 900.8 ( LE01168878 https://en.herbariumle.ru/?t=occ&id=139067, analytical photos and drawings LE01123221 https://en.herbariumle.ru/?t=occ&id=136994, LE01123474 https://en.herbariumle.ru/?t=occ&id=138592) collected in Ha Giang Province, Quan Ba District, Tung Vai Commune, Thung Pang Village , around point 23º04ʹ38.6ʺN 104º56ʹ06.8ʺE, steep rocky slopes near hill top composed with stratified highly eroded limestone at elevation 1000–1100 m a.s.l., remnants of primary evergreen broad-leaved mossy very humid forest, epiphyte, 17 October 2018 , L. Averyanov , Nguyen Sinh Khang , T. Maisak, Truong Duc Thieu. VIETNAM, Ha Giang, 11 08 2022 , Truong Ba Vuong , BV 1609 (photo LE01123481 https://en.herbariumle. ru/?t=occ&id=140370) .

Figures

FIGURE 1. Cleisostoma aspersum (Rchb.f.) Garay. A. Flowering plant. B. Apex of young and old leaves. C. Portion of inflorescence. D. Pedicel and ovary. E. Intact flowers, side view and view from behind. F. Intact flowers, frontal view, side view and view from behind, ovary removed). G. Column and lip, frontal and half side views. H. Lip, side view. I. Lip, view from back. J. Flattened lip, inside surface, front wall of spur removed. K. Flattened lip, outside surface, view from back, front wall of spur removed. L. Front wall of spur, inside surface. M. Sagittal section of pedicel, ovary and flower. N. Anther cap, side view, view from above and from below. O. Pollinarium, views from different sides. All photos made from the specimen VR 900.8, photo correction and design by L. Averyanov and T. Maisak.

FIGURE 2. Cleisostoma aspersum (Rchb.f.) Garay. A. Flowering plant. B. Intact flower, side and frontal views. C. Column and lip, frontal view. D. Column and lip, frontal view, anther cap, pollinarium and frontal lip wall removed. E. Frontal wall of the lip, view from inside. F. Column and lip, side view. G. Column and lip, sagittal section, anther cap and pollinarium removed. H. Anther cap, views from different sides. I. Pollinarium, views from different sides. All drawings made from the specimen VR 900.8 by L. Averyanov and T. Maisak.