Cleisostoma schoenorchaefolium Kumar & S.W.Gale, 2018

Kumar, Pankaj, Gale, Stephan W., Phaxaysombath, Thatsaphone & Fischer, Gunter A., 2018, Cleisostoma schoenorchaefolium (Orchidaceae: Vandeae: Aeridinae), a new species from Lao PDR, Phytotaxa 374 (2), pp. 155-161 : 157-160

Cleisostoma schoenorchaefolium Kumar & S.W.Gale , sp. nov. (ເອອງສອຍມະນດອກນນ; Figs. 1 , 2 )

Type :— LAOS. Xayaboury Province : Parklai District , Mouang Pa Village, Pha Pheung Mountain, 30 June 2016, 455 m, Fischer, Kumar, Phaxaysombath & Sysouphanthong HNL-KFBG 0729 (holotype: HNL; isotype: KFBG) .

Cleisostoma schoenorchaefolium is clearly distinguished from all other known members of the genus by its semi-terete, subulate leaves, septate (two-chambered) spur and complex pollinarium structure. Superficially, the new species most closely resembles C. chantaburiense of section Complicatum in having an elongated, scrotiform spur and a similarly structured pollinarium, but it can be differentiated on the basis of its semi-terete (versus terete) leaves, septate (versus aseptate) spur with an inverted v-shaped (versus finger-like) callus on the back wall and wingless (versus winged) column.

Pendent-arching epiphytic herb. Roots vermiform, branched, often thicker than the stem, up to 20 cm long, 3.0 mm in diameter. Stem terete, branched, up to 50 cm long, 1.5–2.0 mm in diameter. Leaves alternate, dark green, distinctly grooved and semi-terete in cross-section, 15.0–24.0 cm long, 2.0– 2.5 mm in diameter, with a persistent sheathing base up to 1.0– 1.2 cm long, apex subulate with a constriction 1.0– 1.5 cm from the tip. Inflorescences lateral, pendent, glabrous, peduncle terete, rachis ribbed, 4.0–5.0 cm long, up to 1.0 mm in diameter, bearing 1 or 2 sterile bracts near the base and up to 5 flowers arranged in a lax raceme. Flowers 1.4–1.7 cm long, 1.0– 1.5 cm across, petals and sepals spreading, dark yellowish green with dark reddish brown spots, column pale yellow. Pedicel and ovary 6.0–7.0 mm long, yellowish green with reddish brown spots, obscurely ribbed. Petals and sepals spotted reddish brown towards basally, yellowish green apically. Dorsal sepal obovate, 6.0–7.0 × 2.0– 2.5 mm, acute, 3-veined, slightly concave. Lateral sepals obliquely obovate, 6.5–7.5 × 3.0– 3.5 mm, obtuse, 3-veined, slightly convex. Petals narrowly obovate, oblique, 5.0–5.5 × 2.0– 2.5 mm, acute, 2-veined, slightly convex, slightly bent backwards. Labellum trilobed, spurred, 7.5–8.5 mm (from tip of spur to tip of midlobe) × 5.0–6.0 mm, minutely white-papillose basally; lateral lobes pointing forwards, 2.5–3.0 × 2.0– 2.5 mm, acute, with an inconspicuous triangular appendage on the apical margin and a prominent wing-like flap near the base; triangular appendage up to 0.5 mm tall, pointing upwards; wing-like flap up to 1.5 × 1.2 mm, apex rounded, pointing inwards; midlobe triangular, 2.0–2.3 × 2.5–3.0 mm, spreading forwards, base constricted, apex slightly notched. Spur slightly scrotiform at apex, pointing backwards, 5.0–5.5 × 2.0– 2.5 mm, longitudinally ridged underneath, septate inside. Column up to 2.5 mm long, up to 2.5 mm wide; rostellum tooth-shaped, truncate at apex; anther cap hemispherical, ca. 2.0 mm in diameter, 1.2–1.4 mm wide across truncate apex; pollinia 4, arranged in 2 units, yellow, held parallel to the viscidium, 0.7–0.8 × 0.6–0.7 mm, each unit comprising one larger and one smaller pollinium, the larger hemispherical and 0.5 mm wide, the smaller discoid and 0.3 mm wide; viscidium collar-shaped, 1.3–1.4 mm wide; stipe attached to top of viscidium, 1.3–1.5 × 1.0– 1.3 mm, broadest basally, flap-like and recurved above, slightly constricted at middle, terminating in a pointed hood 0.4–0.5 mm long and to which the pollinia are attached on both sides.

Flowering:— July–August.

Habitat:— Epiphytic on trunks of small trees in semi-evergreen forest on limestone mountains.

Etymology:— The epithet ‘ schoenorchaefolium ’ refers to the morphology of the leaves, which look similar to those of certain species of Schoenorchis Reinwardt (1825: 5) , such as S. juncifolia Blume (1825: 361) .

Taxonomic notes:— Cleisostoma schoenorchaefolium is distinguished by the unique morphology of its leaves, which are longitudinally grooved and so not fully terete and as such unlike those of any of the truly terete-leaved members of the genus. Superficially, its flower resembles those of C. chantaburiense Seidenfaden (1975: 70) , but the new species can be distinguished on the basis of leaf morphology (semi-terete with subulate apex versus terete with rounded apex), column morphology (wingless versus with rounded wings), spur morphology (septate and 2-chambered versus aseptate), and the shape of the callus on the back wall of the spur (inverted v-shaped and apically pointed versus divided into two curved, finger-like projections).

The subulate leaf apex of C. schoenorchaefolium is an unusual character in Cleisostoma that is otherwise found only among species of C. section Subulatum Seidenfaden (1975: 23) . However, all members of that section possess flattened leaves. In addition, they have a simple, linear or clavate stipe borne on a tiny, disk-like viscidium, and their anther cap is beaked.

The septate, two-chambered spur of C. schoenorchaefolium is also unusual, having previously been described only in C. elegans , a member of C. section Mitriformes Seidenfaden (1975: 45) . However, members of that section are terete-leaved, their stipe is mitre-shaped, their viscidium is disc-shaped, their labellum has a clavate midlobe and rounded side lobes and the callus on the back wall of the spur is inverted, y-shaped and papillose.

Conservation assessment:— Despite comprehensive surveys in the area, fewer than 20 individuals were seen at the type locality on Pha Pheung Mountain in Xayaboury Province, presently the only known locality for this species. The known area of occurrence (AOO) therefore amounts to just 4 km 2, using a grid cell of 2 × 2 km in GeoCAT ( Moat 2007). The karst landscape of northern and central Laos is increasingly under threat for quarrying and cement production ( Gale et al. 2018). At present, only 10% of the Lao limestone belt is under statutory protection ( Day & Urich 2000, Delang et al. 2013), despite it harbouring disproportionately great phytodiversity ( Clements et al. 2006, Kumar et al. 2016, Li et al. 2018). Additionally, illegal collection for the horticultural trade remains an intense threat ( Schuiteman 2013). We therefore project future decline in population size and habitat quality. Hence, based on IUCN (2018) guidelines, the new species is assessed as critically endangered (B1+B2ab(iii,v); C2a(i); D).

Figures

FIGURE 1. Cleisostoma schoenorchaefolium. A. Plant. B. Front view of flower. C. Oblique view of flower. D. Side view of flower. E. Inflorescence. F. Labellum, flattened and with spur cut longitudinally to show septum and two internal chambers. G. Dorsal sepal. H. Petal. I. Lateral sepal. J. Front view of stipe. K. Top view of stipe. L. Side view of stipe. M. Pollinarium. N. Callus on the back wall of spur. O. Ventral view of anther cap with pollinia. P. Dorsal view of anther cap. Photograph by Pankaj Kumar (A, F–P) & Thatsaphone Phaxaysombath (B–E).

FIGURE 2. Cleisostoma schoenorchaefolium. A. Plant. B. Leaf apex. C. Transverse section of leaf. D. Inflorescence. E. Oblique view of flower. F. Side view of flower. G. Front view of flower. H. Callus on the back wall of spur. I. Dorsal sepal. J. Petal. K. Lateral sepal. L. Labellum, flattened and with spur cut longitudinally to show septum and two internal chambers. M. Side view of stipe. N. Ventral view of stipe. O. Top view of stipe. P. Pollinarium. Q. Ventral view of anther cap with pollinia. R. Dorsal view of anther cap. Drawn by Pankaj Kumar from HNL-KFBG 0729.