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Bulbophyllum section Papulipetalum Schltr., Repert. Spec. Nov. Regni Veg. Beih. 1 (1913) 700, 769. Type species: Bulbophyllum papulipetalum Schltr.
Small to medium-sized epiphytes. Rhizomes (rather) short-creeping (patent to stiffly pendulous in Bulbophyllum ellipticifolium); rhizome bracts thin, surface approx. glabrous to minutely colliculate, caducous and weathering to a dense woolly mass (not in Bulbophyllum ellipticifolium) (with the veins slightly more persistent). Roots sprouting mainly below the pseudobulbs (mainly near to the base of the rhizomes, growing backwards towards the substratum over or alongside the rhizome in Bulbophyllum ellipticifolium), glabrous or slightly and minutely hirsute locally. Pseudobulbs small to conspicuous compared to the size of the plant, 1-leafed, with shoots sprouting at its basal node and free, or fused to the pseudobulb over a very short distance only. Leaves persistent, thick, veins inconspicuous. Inflorescences sprouting at or somewhat above nodes along the length of the rhizome, usually densely fasciculate, 1-flowered. Peduncle shorter than the pseudobulbs to longer than the leaves, peduncle bracts 2—3, scattered along the peduncle. Flowers per sympodium 1 open at a time; floral bracts tubular; pedicel with the basal node well above the attachment of the floral bract, longer than the ovary. Sepals free; the laterals 1—1.4 times as long as the median; 0.6—2.2 cm long, elliptic to (ob-)ovate to triangular, obtuse to short-acuminate, margins entire, glabrous to minutely papillose or ciliolate in, thin to rather thick, 3—5-nerved, surface glabrous or (finely) papillose to hirsute adaxially. Petals free, 0.17—0.45 cm long, spathulate, oblong, or elliptic to (ob-)ovate to triangular, obtuse to acute, margins approx. entire, glabrous to papillose to ciliolate (glandular-ciliate in Bulbophyllum longipedicellatum); thin, 1-nerved, glabrous or adaxial surface papillose or hirsute (distally). Lip mobile on a thin ligament, without auricles near the ligament, undivided, 0.12—0.8 cm long, elliptic to ovate, oblong, or hastate, margins approx. entire and glabrous, surface glabrous or partly papillose; adaxially without ridges, or with two (more or less converging) ridges in approx. flexural position. Column with rostellum front receding in between the stelidia; stigma slit-like to wide, rounded, without keels inside, not protruding proximally; column foot not or hardly widening nor thickening towards its top, free part short, without lateral teeth at the tip; stelidia distinctly shorter to longer than 1/2 of the length of the column; distinct, triangular to subulate, with or without a patent to antrorse deltoid, obtuse tooth along the upper margin, with at most a slight, rounded widening present along the lower margin; anther with a high rounded crest, front not concave, front margin not drawn out; pollinia 2, or 4 with the innerones more than half as long as the outer ones, without appendages.
New Guinea: 23 taxa. Altogether 24 provisionally accepted taxa (29 names): New Guinea, West Pacific.
Genus Bulbophyllum section Papulipetalum can be recognised by the rhizome scales which weather into a dense, woolly mass because of the presence of numerous spiral vessels. This character is also found in a single species with a widened column foot (indet. NGF 38950), which is therefore included in section Polymeres. The pseudobulbs are often ‘bottle-shaped: a wide, ovate basal part drawn out into a thin, stem-like top. Vegetatively, Bulbophyllum ellipticifolium is aberrant in having patent rhizomes; their morphology combines characters not found together in section Polymeres (new shoots not fused to or perforating the pseudobulb, but the rhizome is largely not covered by bracts and slightly fleshy), but similar to e.g. Bulbophyllum acanthoglossum of section Codonosiphon. Many species of section Papulipetalum with more or less subulate stelidia have glandular-papillose, mucus-excreting stelidia tips.
Morphologically, section Papulipetalum is close to section Polymeres through species as Bulbophyllum debruynii, which is here included in the latter. Section Papulipetalum differs in having a not or hardly widened column foot, without lateral teeth or wings. It differs from section Brachypus in the woolly rhizome bracts, free petals (not proximally fused to the column); it differs from the group of Bulbophyllum lineolatum within section Brachypus also in having triangular or subulate, but not strap-shaped stelidia.
Bulbophyllum section Papulipetalum in New Guinea contains the following 22 species and 2 varieties:
Bulbophyllum hians var. alticola
Bulbophyllum longipedicellatum var. gjellerupii