Bulbophyllum sondangii Vuong & Aver. A. Flattened 2023, sp. nov.

B. sondangii Vuong & Aver., sp. nov. (Fig. 1)

Type:— VIETNAM, Lam Dong Province, Trai Mat Town, epiphyte on tree trunk, in broad-leaved forest around Hang Cop Waterfall at elevation about 1343 m a.s.l., 19 June 2020, Truong Ba Vuong, Phan Trong Quyet, BV 704 (holotype, VNM 00043100!).

Paratypes:— VIETNAM, Lam Dong Province, Lac Duong District, remnant forest around Da Sar Commune at elevation about 1487 m a.s.l., 25 June 2022, Truong Ba Vuong, Phan Trong Quyet, BV 1610 (VNM 00069964), BV 1611 (VNM 00069965!).

Etymology: —The species is named after Dr. Dang Van Son (Curator of the VNM Herbarium, Institute of Tropical Biology, Vietnam), Truong Ba Vuong’s PhD advisor, for his immense knowledge and contribution to plant taxonomy.

Description:—Habit creeping perennial epiphytic herb. Pseudobulbs 1-leaved, yellowish- green, ovoid, slightly oblique, 2–3 cm tall, distant on creeping brown rhizome, covered by brownish bracts. Leaves petiolate; petiole 1–2 cm long, slightly curved; leaf blade oblong, 10–15 cm long, 2–3 cm wide, obtuse and slightly retuse. Inflorescence arising from the base of pseudobulbs, ascending and erect; peduncle yellowish-green, with many purple marks, 20–23 cm long, at base with 1–2 overlapping, tubular bracts, above with 3 distant tubular bracts; rachis 1–1.5 mm long, bearing 12 flowers in form of sub-umbellate raceme; floral bracts narrowly triangular ovate t, dull yellowish, flushed with red at base, 6–7 mm long, 3–3.5 mm wide, obtuse; pedicel and ovary yellowish-green with many reddish marks, 1.5–1.6 cm long. Flower s opening simultaneously; median sepal pale yellowish green with many dark red spots; lateral sepals yellowish to reddish, more dark at base, with many red-reddish spots; petals yellowish with 3 red purple stripes; lip reddish purple, with many dark red dots adaxially, yellow at base. Dorsal sepal almost circular, 5–6 mm long and wide, with a short seta and few stiff hairs at apex. Lateral sepals narrowly obovate in outline, oblique, 23–25 mm long, 5–6 mm wide, acute, at base twisted, upper margin connate but free at base and apex, lower margin free. Petals triangular ovate, 4–5 mm long, 3–3.5 mm wide, slightly oblique, with short seta and few short hairs at apex. Labellum triangular ovate, fleshy, glabrous, ca. 4 mm long, 2 mm wide, strongly curved, margin curved, blunt at apex; adaxially at base with median swollen callus, somewhat oblate in apical part; abaxially with two longitudinal keels coming from the base to apex; auricle spreading horizontally, obscurely rectangular, truncate. Column stout, broadly conoid, erect, ca. 3 mm tall, lateral margins basally with triangular wings, rounded at apex; column foot 2–2.5 mm long, in apical part slightly up curved; stelidia triangular, slender and subulate at apex, pointing forward and slightly down curved; stigma obovate, concave; anther cap ovoid, ca. 1 mm long, frontal margin broad, rounded, finely papillose; pollinia 4, narrowly ovoid, laterally flattened. Fruit not observed.

Habitat and phenology: —Observed as a trunk epiphyte in primary evergreen, broad-leaved forests at an of elevation 1300–1500 m a.s.l., along the stream of Hang Cop waterfall. Flowers are seen blooming during June– August.

Proposed conservation status:—The species is reported from only two sites, which are very close to each other at Da Sar and Hang Cop waterfalls (Lam Dong Province) with the total area of occurrence (AOO) of less than 4 km 2. The first sub-population occupies the Hang Cop Waterfall tourist recreation area which is highly influenced by the tourist activity. The second sub-population is a highly degraded forest near the local settlements. Both sites are considered as unique locations owing to independent threat at both places. And, there is observed decline in the quality of the habitat. Under following circumstances, the species can be assessed as Endangered, EN B2ab(iii) based on Red List IUCN guidelines (IUCN 2022).

Taxonomic notes:—The newly described species closely resembles Bulbophyllum andersonii (Figure 2). Both species share characters such as an elongated peduncle and setose median sepal and petals; however, B. sondangii differs by having a short apical seta on median sepal and petals, almost entire petals and lip with auricles. The comparison of morphological characters of new species and its closest species are presented in Table 1.