Cleisostoma tatonii Aver. & V.C.Nguyen, 2022

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 : 47-48

Cleisostoma tatonii Aver. & V.C.Nguyen , sp. nov.

( Figs. 3 , 4 )

Type: — VIETNAM. S Vietnam, Kon Tum Province, Ngoc Linh Mountains , 13 September 2021, Ta Ton, Nguyen Van Canh , AL 1591 (holotype LE01169337 https://herbariumle.ru/?t=occ&id=142648, analytical photos and drawings made from specimen used for preparation of the type specimen LE01122992 https://en.herbariumle.ru/?t=occ&id=110358, LE01123534 https://en.herbariumle.ru/?t=occ&id=141837) .

Etymology: —Species name honors its discoverer, an orchid enthusiast, Mr. Nguyen Ta Ton.

Description:—Herb perennial monopodial epiphytic. Stem simple or basally few branching, semi-woody, erect or ascending, (4)5–8(10) cm long, covered throughout by leaf sheaths, with (5)6–8(10) leaves, in basal half with few thick wiry flexuose white roots; internodes (6)7–10(11) mm long. Leaves subdistichous, sessile, dorsiventral, leathery, somewhat succulent, straight or arching, oblong, (14)15–18(20) cm long, (1.6)1.8–2(2.2) cm wide, unequally bilobed at apex, with distinct articulation at the base. Inflorescence lateral raceme or few branching panicle, (8)10–12(14) cm long, scape and rachis dark greenish gray; scape 1–2 cm long, pendulous, panicle branches 1–3(4), (4)6–8(10) cm long; rachis (4)5–8(10) cm long, more or less straight, with many spirally arranged, dense to subdense flowers. Floral bracts dark gray greenish, minute, triangular, acute, 1–1.2(1.4) mm long, 0.6–0.7 mm wide. Pedicel and ovary terete, longitudinally slightly grooved, (4.5)5–6(6.5) mm long, (0.7)0.8(0.9) mm in diameter, light green, slightly broadening at the base, glabrous or with few scattered scurfy brownish hairs. Flowers widely opening, (6.5)7–8(9) mm across; sepals and petals somewhat fleshy, spreading, dark purple brown, with pale yellowish median vein and yellowish margin; lip yellow with brown purple marks on the lip lobes and spur; column yellow flushed with brown purple at apex; anther cap dark brown purple with two lateral yellowish spots. Sepals narrowly ovate to ovate, concave, rounded at apex, (3.4)3.6–4(4.2) mm long, (1.2)1.4–1.8(2) mm wide, at the base with few scattered scurfy brownish hairs; median sepal distinctly cucullate; lateral sepals somewhat oblique. Petals narrowly obovate to broadly oblanceolate, glabrous, blunt to obtuse at apex, (2)2.2–2.4(2.6) mm long, (0.5)0.6–0.8(1) mm wide, slightly oblique. Lip spurred, (6.2)6.5–7.5(7.8) mm long (from spur apex to the apex of epichile), 3-lobed; side-lobes triangular, erect, 0.5–0.7 mm long, inside at the base with small round callus and in distal part with erect subulate processus (1)1.2–1.4(1.6) mm long; median lobe fleshy, arrow shaped, (1)1.2(1.4) mm long, (4.2)4.4–4.6(4.8) mm wide, with 3 small triangular lobules at apex and 2 large ensiform, lateral, back directed acute lobules (1.4)1.6–1.8(2) mm long; spur shortly cylindrical, almost parallel to ovary or slightly upcurved, (3)3.2–3.4(3.6) mm long, (1)1.2–1.4((1.6) mm in diameter, round at apex, without longitudinal septum inside. Spur back-wall inside with Y-shaped callus, (1.6)1.8(2) mm wide, (0.7)0.8–1(1.1) mm long, shortly hairy or densely glandular at base. Spur front-wall inside with two hairy or densely glandular lateral calli, allied to the apex of back-wall callus and almost closing (together with back-wall callus) the entrance to the spur; the base of median lobe with short glabrous rising longitudinal keel. Column short, broad, stout, shortly cylindric, (1.7)1.8–2(2.1) mm tall and wide, at apex on each side with dense, half-globular bunch of white trichomes 0.5–0.6 mm in diameter, near apex at front with rostellum supporting large rectangular concave viscidium; stigma at front of column, in form of large prominent disk, (1.8)2–2.2(2.3) mm in diameter, with small obscurely triangular hollow near proximal margin. Anther cap helmet shaped, 0.5–0.6 mm tall, (1.1)1.2–1.4(1.5) mm wide, with large gibbous, concave, narrowly triangular beak, (1)1.1–1.2(1.3) mm long. Pollinia 2, each incompletely split into 2 half-globular bodies. Stipe (tegula) in form of narrowly triangular, conduplicate scarious stalk (1.2)1.4–1.5(1.6) mm long; viscidium large, in form of rectangular concave plate, 0.9–1.1 mm long, 0.7–0.8 mm wide (being flattened). Fruit almost sessile, narrowly ellipsoid, slightly ridged capsule, (9)10–12(13) mm long.

Ecology and phenology:—Epiphyte. Primary evergreen broad-leaved and mixed forests on granite at elevation 1000–2000 m a.s.l. Flowers in September.

Distribution:— VIETNAM. S Vietnam, Kon Tum Province, Ngoc Linh Mountains. Endemic.

Conservation status:—Despite many-years, special field searches of professional botanists and numerous orchid enthusiasts only few samples of this extremely rare species were found in one location. Being into consideration vast deforestation in Ngoc Linh Mountains it may be expected that this species stands on the verge of full extinction in the nature. According to available data, having one population with EOO and AOO less than 100 km 2 and 10 km 2 respectively, expected coming extinction, and very small population with less than 50 mature individuals, it may be preliminarily assessed as globally Critically Endangered – CR (B1a,b(ii,iii), B2a,b(ii,iii); C1a(i,ii), C2a(i,ii); D).

Notes:—According to plant and floral morphology, the new species has rather isolated, intermediate taxonomic position between C. sect. Cleisostoma ( Seidenfaden 1975: 10) and C. sect. Paniculata Seidenfaden (1975: 34) . The structure of its pollinarium has triangular conduplicate stipe with large rectangular longitudinally concave viscidium, very large discoid stigma broader than the column itself, dense bunches of white hairs at the column apex, and dense inflorescence are features unique in the genus ( Averyanov et al. 2015). We see no any close relatives for our plant among its congeners.

Figures

FIGURE 3. Cleisostoma tatonii Aver. & V.C.Nguyen, sp. nov. A. Flowering plant. B. Inflorescence. C. Portion of inflorescence. D. Intact flower, frontal view. E. Intact and flattened flowers, side views. F. Median sepal, abaxial side. G. Lateral sepals, abaxial and adaxial sides. H. Petals, abaxial and adaxial sides. I. Flattened flower, frontal part of the lip (including spur) removed. J, K. Frontal part of the lip (including spur), view from inside. L. Intact column, frontal, half-side and side views. M. Anther cap, views from different sides. N. Pollinarium. O. Pollinarium stalk (tegula), views from different sides. P. Pollinia. All photos made from the type specimen AL 1591 by Nguyen Van Canh and L. Averyanov, photo correction and design by L.Averyanov and T. Maisak.

FIGURE 4. Cleisostoma tatonii Aver. & V.C.Nguyen, sp. nov. A. Flowering plant. B. Leaf, adaxial side. C-E. Intact flower, frontal, halfside, and side views. F. Sagittal lip section. G. Flattened flower, frontal part of the lip (including spur) removed. H, I. Frontal part of the lip (including spur), view from inside and outside. J. Anther cap, views from different sides. K. Pollinarium, frontal view and view from back. L. Pollinarium stalk (tegula), views from different sides. All drawings made from the type specimen AL 1591 by L. Averyanov and T. Maisak.