Orchidantha megalantha Škorničk. & A.D.Poulsen, 2017

2. Orchidantha megalantha Škorničk. & A.D.Poulsen View in CoL , sp. nov. — Fig. 4 View Fig , 5 View Fig

Similar to O. holttumii in overall habit, the petiolate leaves, and the claw-like arrangement of the petals, but differing in the larger flowers with slightly unequal sepals (vs equal), dorsal sepal 14–15 × 4–4.1 cm, lateral sepals 15–16 × 3.7–3.9 cm (vs c. 9 × 2 cm), labellum 12.5–13.5 × c. 4 cm (vs 7 × 2 cm) and purple stigma (vs white). — Type: A. D. Poulsen & Biogo Mutang 2073 (holo SAR; iso AAU, Sarawak Biodiversity Centre, SING), Malaysia, Sarawak, Mulu NP, shortcut trail between the Penan village and Gunung Mulu, N4°02ʹ E114°49ʹ, 30 m elevation, 17 July 2003, flowering GoogleMaps .

Etymology. The epithet refers to the large flowers relative to other species of the genus.

Robust clump-forming herb, up to 1 m tall, c. 14–15 leaves per shoot; juvenile plants as well as adult plants with distinctly petiolate leaves; leaves to 1.3 m long (including petiole), petiole up to 55 cm; lamina unequal, elliptic, to 75 × 15.5 cm, base asymmetrical, attenuate, apex narrowly attenuate. Inflorescence on a slender, branched, pale to cream-coloured, burrowing stem with prominent bracts and/or their scars; prophyll triangular, two-keeled, 22–23 mm long, 13–14 mm wide at base; second bract 30–42 mm long, c. 15 mm wide at base, shortly cuspidate; third bract 45–60 mm long, c. 20 mm wide at base, shortly cuspidate; floral bract burrowed in the soil at base, apex appearing above the soil, green with a rich rusty-red tinge apically when exposed above ground, 90–130 mm long, c. 32 mm wide. Flower smell not recorded; pedicel c. 30 mm long; ovary extension c. 100 mm long, cream-white at base to green-yellow apically; sepals yellow-green (dorsal sepal with a slight rusty-red tinge particularly towards the sides), narrowly elliptic, cuspidate, glabrous, entire; dorsal sepal 140–150 mm long, 40–41 mm wide (cusp c. 3 mm); lateral sepals overlapping, often crossing and supporting the labellum, 150–160 mm long, 37–39 mm wide, cuspidate at apices (cusp c. 5–6 mm); lateral petals overlapping at base covering stamens and style, dark purple, irregularly elliptic, cuspidate (cusp 3–4 mm, recurved), 40–42 mm long, 11–12 mm wide, outer margin undulate at the distal half; labellum elliptic with strongly raised midrib (c. 4 mm wide), 125–135 mm long (including a 5–10 mm long acuminate tip), c. 40 mm wide, dark purple throughout but slightly fading towards apex, sides strongly reticulate with vertical lines more pronounced, sides and margins of labellum undulate and involute distally. Stamens c. 25 mm long; filaments 7–8 mm long, 2 mm broad, cream-white with slight purple tinge; anther thecae introrse, 14–15 mm long, longitudinally dehiscent throughout the length. Style cream-white, c. 21 mm long; stigma c. 17 mm long, deeply 3-lobed, dorsal surface and stigma lobes tinged purple, conduplicate, margin membranous, minutely laciniate, median lobe c. 11 mm long; lateral lobes c. 10 mm long; viscidium V-shaped and extending from the base to about half of the lateral lobe (pronounced in side view); side of the V-shape c. 9 mm long.

Distribution — So far known only from the type locality.

Habitat & Ecology — Growing on a sandy hill c. 300 m from a limestone cliff. Flowering observed in the field in April and July.

Conservation status — Orchidantha megalantha is reported from one population on a sandy shallow hill with several individuals within a national park area with no perceived threats. As the number of mature individuals is <1 000, it may be considered ‘Vulnerable’ (VU) D1 ( IUCN Standards and Petitions Subcommittee 2017).

Note — Orchidantha megalantha resembles O. holttumii K.Larsen ( Fig. 6 View Fig ) by the height not exceeding 1.5 m and the presence of petiolate leaves in both young and adult individuals. The shape of the flower is also similar; the two lateral sepals overlapping below the labellum and the dorsal sepal arching over it, resulting in claw-like appearance of the flower. The flower of O. megalantha is, however, twice as big as that of O. holttumii , the sepals are bright yellow-green and stigma is purple (compared to pale greenish sepals and white stigma in O. holttumii ). So far, all species of Orchidantha are known to be very restricted in their distribution ( Sakai & Inoue 1999). The difference in the size and colouration of the flower is likely an adaptation to a specific pollinator, most likely a dung beetle, as previously reported for other species of Bornean Orchidantha ( Sakai & Inoue 1999, Pedersen 2001).