Bulbophyllum bukitrayaense Yudistira & Mustaqim, 2025

Yudistira, Yuda R., Randi, Agusti, Joharudin, Didin & Mustaqim, Wendy A., 2025, Contributions to the orchid flora of Kalimantan II: A new Bulbophyllum sect. Macrocaulia from Mount Bukit Raya, Indonesia, Phytotaxa 700 (3), pp. 251-256 : 253-255

Bulbophyllum bukitrayaense Yudistira & Mustaqim sp. nov. ( Fig. 1 )

Type:— INDONESIA. Kalimantan Barat Province, Sintang Regency, Serawai Subdistrict, Rantau Malam Village, Bukit Baka Bukit Raya National Park, trail to summit of Mount Bukit Raya, Linang camp [0°38’44.9”S 112°39’26.0”E], 1320 m.elev., 7 July 2024, Yudistira & Mustaqim YRY064 (holotype: WAN!-spirit).

Diagnosis:— Bulbophyllum bukitrayaense is morphologically similar to B. scabrum Vermeulen & Lamb (1988: 46) in having the lower surface of the labellum with two times approaching margin undulation, but the new species has labellum with larger length per width index (2.2 times vs up to 1.7 times) and coarsely rugose upper ¼ surface (vs smooth), broadest point in a non expanded state at half of its length (vs upper third), and ovary covered by papillose-muriculate indumentum (vs glabrous). It is also similar to B. ovalifolium ( Blume 1825: 318) Lindley (1830: 49) but differs in having the rocket-shaped labellum (vs elliptic to ovate), presence of approaching margin undulation on the lower surface of the labellum (vs absent), ovate petals (vs oblong), and the presence of papillose-muricate indumentum in the ovary (vs absent). ( Table 1).

Small, creeping epiphyte herbs. Roots below the pseudobulb, flexuous c. 0.5 mm diam., white. Rhizome creeping, c. 1 mm across, section between pseudobulb 0.5–2 mm with thin clustering papery sheath in young pseudobulb, c. 2–4 mm long, caducous. Pseudobulb fused to the rhizome, pale green, ovoid to elliptic, 4–7 × 3–4 mm, glabrous.

Leaf : petiole canaliculate 0.5–1 mm long, lamina obovate- or elliptic-oblong, 10–15 × 2–4 mm, base cuneate, apex mucronate-apiculate, entire, glabrous. Inflorescence arising from the base of the pseudobulb, 1-flowered; flower 1.0– 1.1 cm broad across lateral sepals, these from arranged in secund raceme, the axis up to 2.5 mm long; peduncle curving, 14.5 mm long, thickened at the base, bracts only basal, up to 1.5 mm long, acute, glabrous, strongly keeled at the back; floral bracts tubular, c. 1.9 mm long, apex obtuse, entire, glabrous. Flowers rather not open widely, 1.0– 1.5 cm wide. Pedicels terete, ovary shallowly channeled, altogether c. 12 mm long, orange, basal nodes 1.7 mm long; ovary papillose-muriculate. Dorsal sepal erect, ovate to elliptic, 6 × 3 mm, margin ciliate, apex acuminate, 3- veins and 2 lateral veins forked, prominent adaxially, obscure abaxially, coarsely papillose in adaxial and abaxial; margin orange similar to veins. Lateral sepals ovate, slightly asymmetric, 11.5 × 6.0 mm, margin ciliate, apex obtuse, apiculate, outer surfaces coarsely papillose, inner surface verrucose; 4 veins and 2 lateral veins forked, veins prominent outside, obscure inside. Petals ovate, rhombiform, c. 0.8 × 0.8 mm, apex obtuse, tip rounded; 1-veined, vein prominent dorsally, orange. Labellum rocket shape in natural shape, oblong, 3.25 × 1.5 mm, index 2.2, broadest at the middle, slightly recurved, concave at the base, with margin erect a the basal ¼, downcurved in the middle, then spreading before abruptly approaching each other toward the upper third, rounded in the apex; basal part sac-like cavity above the ligament, its margin bordered by two blunt ridges, running toward the lower third, approaching but not anastomosing; upper ¼ coarsely verrucose, glabrous elsewhere. Column including stelidia c. 0.8 mm, stigma bluntly quadrangular, with a blunt callus at its base, column foot c. 1 mm long. Stelidia narrowly triangular, facing upwards, c. 0.2 mm long, lower margin c. with shallow and broad wing, c. 0.05 mm. Anther cap not seen. Pollinia 2.

Phenology: —Flowering in the wild observed in July, fruiting unknown.

Distribution and habitat: —Endemic to Kalimantan: so far only known from the type locality in Mount Bukit Raya ( Fig. 2 ). The species grows as epiphyte on the mossy tree trunk ( Fig. 3 ), mid-montane forest on a slope close to the summit area, at an elevation of 1,320 m.

Etymology: —The epithet refers to Bukit Raya, the name of the mountain where the species was found for the first time.

Notes: —The section Macrocaulia (Blume) Averyanov (1994: 279) in Borneo, where this new species belongs, consists of 42 species with half of them being endemics. It is characterized by the plants having pseudobulb relatively large compared to the whole size of the plants which adnate to the rhizome and flowers with entire petals and labellum without transverse ridge at the base as well as the labellum with the absence of a transverse ridge at the labellum base, labellum connate with and entire petals ( Vermeulen et al. 2015). The number of species is much larger than the surrounding island in Sundaland, i.e. Sumatra (11 species; Comber 2001, Yudistira et al. 2024), Peninsular Malaysia (13 species; checked and added from 11 mentioned Seidenfaden 1992), or Java (5 species; checked from 7 mentioned in Comber 1990).

Bulbophyllum bukitrayaensis and B. scabrum , as the most morphologically similar species, has an affinity to the variable and widespread Bulbophyllum ovalifolium (see Atmaja et al. 2017 and Metusala et al. 2020 for discussion regarding morphological variations of B. ovalifolium ). Vermeulen et al. (2015) placed the materials that have ovaterhombiform petals from the B. scabrum - B. ovalifolium complex as B. scabrum , a species distributed in Sabah and Sarawak from 1500 to 2100 m asl. Based on this reason, the new species is closer in morphological similarity to B. scabrum and separated as a new species with the morphological characters mentioned in the diagnostic. Besides that, B. scabrum also has short inflorescence and always has constant, single, inflorescence per node instead of racemosely arranged inflorescence in B. bukitrayaensis .

Figures

FIGURE 1. Morphology of Bulbophyllum bukitrayaense. A. Plant. B. Axis of inflorescences. C. Inflorescence. D. Flowers, frontal view. E. Flowers, abaxial. F. Flowers, side-view. G. Dorsal sepal. H. Lateral sepals. I. Petals. J. Flowers with perianth removed. K. Labellum, abaxial. M. Labellum, adaxial. N. Labellum, lateral view. O. Ovary and column. P. Column, frontal view. Q. Pollinia. Photographs by Yuda R. Yudistira from the holotype.

FIGURE 2. Geographical distribution of Bulbophyllum bukitrayaense.

FIGURE 3. Bulbophyllum bukitrayaense (A) in its habitat alongside Bulbophyllum succedaneum J.J.Sm. (Smith 1927: 67). Photograph by Wendy A. Mustaqim.