Dendrobium fuscifaucium Souvann. & Kumar, 2022

Souvannakhoummane, Keooudone, Kumar, Pankaj & Phonepaseuth, Phongphayboun, 2022, Dendrobium fuscifaucium (Orchidaceae: Epidendroideae: Dendrobieae), a new Laotian species only known in cultivation, Phytotaxa 541 (3), pp. 285-290 : 286

Dendrobium fuscifaucium Souvann. & Kumar , sp. nov. ( Figs 1 , 2 )

Type:— LAOS. Vientiane Province: Kasi District, under cultivation by Chanthasone Inthavong at Oda Orchid Nursery , voucher collected on 24 July 2021, Souvannakhoummane KS 1400 (holotype: HNL, HNL0009890) .

Dendrobium fuscifaucium is similar to Dendrobium hekouense in having clustered fusiform to ellipsoid stems, but it can be differentiated ( Table 1 ) on the basis of colour of sepals and petals (pink with purple veins vs. white with faint purple veins), labellum hairs (double length in new species), labellum disc colour (chocolate brown vs. dark violet), labellum outline (lacking distinct front lobe vs. with distinct front lobe marked by constriction on both sides), labellum frontal margin (irregularly fimbriate vs. irregularly denticulate), labellum callus (narrow-lamellar vs. broadly convex), column (broadly elliptic and puberulent towards margin vs. narrowly elliptic and glabrous) and mentum (almost straight vs. incurved).

Epiphytic perennial herbs. Rhizome 2–3 mm diameter, grey, covered with scales. Stems 3–5 mm distant on the rhizome, fusiform, narrowly ellipsoid, 5–15 mm long, 2–5 mm diameter, shortly stalked, with 2–3 nodes, internodes 1–5 mm long. Leaves narrowly elliptic to oblong-elliptic, 2.0–5.2 × 3.5–8.0 mm, apex acute to round, base shortly cuneate, margin entire; adaxial dark green, glabrous; abaxial pale green with purple spots; midrib prominent on abaxial surface. Petiole ca. 1 mm long, glabrous, pale green with prominent purple veins. Bladeless sheaths 1–3, green with grey longitudinal fibrous crests, glabrous; leaf sheaths green with dark green longitudinal markings, glabrous. Inflorescence borne on leafless stem, subterminal, 1-flowered; peduncle 1–2 mm long, with 1 cup-shaped sheath at base, glabrous, grey when dried; bract triangular-ovate, 1.5–2.2 mm long, pale green to grey; pedicel and ovary 6.5–7.0 mm long, glabrous, pale green to dark brown. Flowers spreading horizontally, sepals and petals cream-pink with a purple vein, outer surface pink to violet, the labellum brown chocolate to claret violet on disc, margin yellow, lateral lobes yellow with a brown to claret violet U-shaped patch, midlobe yellow at base with pale violet to pink apex. Dorsal sepal ovate, 6.0–6.5 × 5.0– 5.5 mm, glabrous, apex acute, margin entire, inner surface cream to pale pink, outer surface pink to violet at base with 5 violet lines. Lateral sepals obliquely triangular-ovate, 6.5–7.0 × 13.0–15.0 mm, glabrous, apex acuminate, margin entire, inner surface cream to pale pink, outer surface pink to violet at base with 5 violet veins; mentum saccate, 9.0–10.0 × 5.5–6.0 mm, slightly incurved, tapering apically, round and bilobed apically, brown to claret violet with green near base. Petals elliptic-ovate, 4.5–6.0 × 3.5–4.0 mm, glabrous, apex acute to round, margin entire, inner surface cream to pale pink, outer surface pink to violet at base with 3–5 violet lines. Labellum pubescent adaxially, trilobed; lateral lobes erect, obliquely triangular, 8.0–9.0 × 3.5–4.0 mm, margins entire but irregularly fimbriate apically; midlobe deflexed, reniform, emarginate, 2.8–3.0 × 9.5–10.0 mm, margins irregularly fimbriate, yellow and cream pink, papillose; brown papillose with callus of two narrow lamellar ridges on disc and base of midlobe. Column 2.0–2.4 × 2.0– 2.5 mm, puberulent towards the margin, glabrous in centre; column foot 7–8 mm long, brown with dark violet, green towards the apex, pubescent towards the margin, almost round apically; operculum conical, densely green, white in front. Capsules oblong-ellipsoid, 10–15 × 5–8 mm, glabrous.

Distribution:— Said (by the nursery owner where this species was found) to be from the limestone mountains in Kasi District, but the authors have been unable to find the plant after multiple attempts. Currently, a living collection of the species is maintained at HNL and the nursery from which the plants were obtained.

Ecology and habitat:— Epiphytic in the deciduous limestone forest. Flowering July, fruiting August– September.

Etymology:— Refering to dark brown colour on the disc of the labellum.

Vernacular name:— ເeື້eϧg໋ennșແລັo [Ueang Sok Ka Lat, chocolate-lipped dendrobium]

Notes:— Dendrobium fuscifaucium is morphologically similar to D. hekouense , D. luoi and D. wangliangii in their epiphytic habit and smaller stature of vegetative parts with comparatively large flowers appearing on leafless stems. However, they can be easily differentiated ( Table 1 ).

Conservation:— Dendrobium fuscifaucium is described based on plants obtained from the nursery. Multiple attempts to find the plants in the wild at the original location in Kasi District have failed. Hence, no assessment can be made. It may be extinct in the wild or come from a site different than that claimed. Further surveys are required.

Figures

FIGURE 1. Dendrobium fuscifaucium. A. Habit. B. Flower, front view. C. Flower, side view. D. Flower, ventral view. E. Young fruit. F. Sepals, petals and column. G. Labellum. H. Anther cap, dorsal view. I. Anther cap, ventral view. J. Anther cap, posterior view. K. Pollinium.All drawn from live plant (KS1400) by K. Souvannakhoummane.

FIGURE 2. Dendrobium fuscifaucium.A–C.Habit.D. Flower, side view. E. Flower, front view. F. Sepals, petals and column.G. Labellum. H. Anther cap, dorsal view. I. Anther cap, ventral view. J. Anther cap, posterior view.All from (KS1400) by K. Souvannakhoummane.