Cleisostoma equestre Seidenfaden (1992: 393)

Averyanov, Leonid V., Thai, Tran Huy, Truong, Ba Vuong, Nguyen, Van Canh, Nguyen, Tuan Hoang, Maisak, Tatiana V., Nguyen, Khang Sinh & Nguyen, Van Khuong, 2022, New orchids in the flora of Vietnam (Orchidaceae, Aeridinae), Phytotaxa 555 (2), pp. 113-135 : 118

Cleisostoma equestre Seidenfaden (1992: 393) .

( Figs. 1 H, I , 2 )

Type: — VIETNAM. S Vietnam, Soviet-Vietnamese Expedition, Province Quangnam – Danang, Da Nang, Son Tra , 09.07.1986, LX-VN 0-14, fl. et coll. in horto 25 11 1987, herbarium prepared by Averyanov L., 1987) – LE (holotype – LE01059075 https://en.herbariumle.ru/?t=occ&id=9915, epitype – LE01059069 https://en.herbariumle. ru/?t=occ&id=9909, photos – LE01088036 https://en.herbariumle.ru/?t=occ&id=46070) .

Habitat, phenology and conservation status. Epiphyte. Broad-leaved evergreen lowland forests on granite at elevation of 50–400 m a.s.l. Fl. June–July. Very rare. Suggested IUCN Red List status – DD.

Distribution. Central Vietnam (Da Nang City Area). Endemic.

Note. This species, very curious for its unusual column and pollinarium structure, was described thirty years ago on the basis of rather insufficient material collected from cultivated plants originating from Son Tra Island. Recently, it was rediscovered on the continent also near Da Nang City in forest of Ba Na Mountain in 20 km to the SW from the locus classicus. The new collection provides additional data on the floral morphology of this extremely rare species, which is presented below in the form of an amended description and fig. 2. More surveys are needed to check the presence of this species in adjoining areas. Accordingly, based on IUCN (2019) C. exuestre should be formally estimated as Data Deficient – DD.

Amended description. Flowers not widely opening, campanulate, (9.5)10–11(11.5) mm across; sepals and petals rather fleshy, glabrous, white with two broad purple-brown longitudinal stripes, or with entirely purple-brown center; lip including spur white, with few purple speckles on lobes, bright yellow at base. Sepals obovate, concave, blunt to obtuse, (6)6.2–6.4(6.5) mm long, (3.6)3.8–4.2(4.4) mm wide, median sepal cucullate, lateral sepals slightly oblique. Petals narrowly obovate, almost flat, blunt to round at apex, (5.4)5.6–6(6.2) mm long, (2)2.2–2.4(2.6) mm wide, slightly oblique. Lip spurred, (6.8)7–7.8(8) mm long (from spur apex to the apex of epichile), 3-lobed; sidelobes broadly triangular, obtuse, forward protruding, 2.4–2.5 mm long and wide at the base; median lobe fleshy, halfglobular, 2–2.2 mm long, 3–3.5 mm wide, forward directed, round or obscurely trilobe at apex, at base with prominent uprising conoid callus; spur saccate, almost parallel to ovary, 4–4.2 mm long, 2.8–3 wide, slightly dorso-ventrally flattened, with round, slightly emarginate apex and incomplete longitudinal septum inside. Back-wall callus in form of large, erect, T-shaped, flattened, papillose outgrowth about (1.6)1.8–2(2.2) mm tall, at apex with two recurved conoid horns, at base connected with fleshy side-lobes by fleshy papillose rollers. Column short, broad, obscurely cubic, (3.6)3.8–4(4.2) mm high, (1.8)2–2.2(2.4) mm wide, at front with small rostellum lobes supporting viscidium horns; stigma in form of transversely oblong hollow. Anther cap helmet shaped, skinny, sac-like, 2.2–2.4 mm tall and wide, without beak. Pollinia 2, each deeply split into 2 half-globular bodies. Stipe (tegula) in form of circular scarious plate 1.8–2 mm in diameter (being flattened), enveloping pollinia in form of narrow funnel after removing anther cap, viscidium in form of two narrow subulate forward directed acute horns 0.8–0.9 mm long.

Studied specimen. Vietnam, Da Nang City Area, Ba Na Mt., evergreen broad-leaved forest at elevation of 300–400 m a.s.l., epiphyte, rare, June 2019, Nguyen Van Canh , AL 1123a (LE01167438 https://en.herbariumle.ru/?t=occ&id=133067, drawings LE01123081 https://en.herbariumle.ru/?t=occ&id=133320, photos LE01123087 https:// en.herbariumle.ru/?t=occ&id=134257).

Figures

FIGURE 1. Ascocentropsis malipoensis. A. Flowering plant (AL 1295), B. Flower, half side view (AL 1187). Chiloschista parishii var. minutiflora. C. Inflorescence. D. Portion of inflorescence with fully open flowers (Nguyen Van Canh, Nguyen Hoang Tuan, s.n.). Chiloschista sweelimii. E–G. Flowering plant, inflorescence and flower, half side view (Nguyen Van Canh s.n.). Cleisostoma equestre. H. Flowering plant, I. Flower, frontal view (AL 1123a). Photos by Nguyen Phi Tam (A), L. Averyanov (B), Nguyen Van Canh (C, D, H, I), and anonymous photo (E–G).

FIGURE 2. Cleisostoma equestre. Details of flower. A. Flower, half-side view. B. Flowers, side view. C. Flower, view from above. D. Flower, view from below. E. Flattened sepals and petals. F. Separated lip, view from above. G. Lip, tangential section, view from below (part with median lobe is removed).H. Lip, tangential section, view from above (part with side-lobes is removed). I. Lip, view from below. J. Separated lip, side view. K. Separated lip, sagittal section. L. Column, frontal view. M. Column, side view. N. Column with half-opened anther cap, pollinarium stipe removed. O. Column with opened anther cap and intact pollinarium. P. Anther cap, frontal view and vied from behind. Q. Pollinarium stipe, adaxial side. R. Pollinarium stipe, abaxial side. S. Pollinarium stipe, half-side view. T. Pollinia. All drawn from the specimen (AL 1123a) by L. Averyanov and T. Maisak).