Large, robust homeophyllous root-climbing liane to 15 m. Eocaul not observed; stem of juvenile shoot to 8 mm diam., weakly angled or subterete in cross section, leaves scattered or congested; stem of mature sterile shoot to 12 mm diam., mid-green, later turning brown, air-drying black-brown weakly four-angled, at first somewhat densely clothed with leaves, early growth often with all leaves directed forwards and the whole appearing imbricated, later with leaves distichous, spreading, stems eventually becoming naked, naked portions with prominent 60 – 80 mm distant nodes; stem of fertile shoot to 5 mm diam., terete to weakly to somewhat prominently angled in cross section, the angles occasionally minutely winged, mostly densely clothed with leaves, older portions naked for approximately half their length, naked portions with prominent nodes to 30 mm distant. Leaves when fresh bright to mid-green adaxially, paler abaxially, air drying dull green to brownish; petiole 50 – 140 x 5 – 15 mm, broadly winged, oblong to obovate-oblong, with 4 – 5 secondary veins per side, base decurrent to clawed, apex truncate, rounded or auriculate; lamina 3 – 180 x 15 – c. 205 mm, ovate to elliptic or lanceolate with 2 – 4 intramarginal veins per side, these arising from the base and either immediately diverging or remaining very close and parallel to midrib and then diverging further along lamina, either reaching the leaf tip or merging into a prominent submarginal collecting vein, additional veins arising obliquely from the midrib, remaining parallel with numerous veins arising from them, base rounded to acute, apex attenuate-mucronate to acute or attenuate, minutely tubulate. Flowering shoot much abbreviated, arising from mostly the middle to distal leaf axils of fertile shoots, sometimes arising on older (foliage) leafless parts, bearing a minute prophyll and a few 5 – 35 mm, sequentially longer cataphylls. Inflorescence solitary; peduncle 40 – 100 x 1.5 – 2 mm, rather stout, erect, dull orange-yellow; spathe 4 – 12 x 4 – 10 mm, ovate, flat to convex, base cordate, clasping the peduncle, apex slightly raised, acute to subacute with a stout mucro, white, somewhat waxy; spadix stipitate; stipe 27.5 – 40 x 2 – 2.5 mm, terete in cross section, erect, straight, pale green; fertile portion 12.5 – 15 x 10 – 12 mm, ovoid-clavate, mid-yellow. Flowers c. 1 – 2 mm diam.; tepals 1 x 0.3 mm, oblong-cymbiform, apex fornicate, triangular, truncate; stamens 1 – 4 x c. 0.5 mm, filaments strap-shaped, thecae c. 0.2 mm diam., yellow; ovary 1 – 1.5 x 0.25 – 0.75 mm, compressed angular-ellipsoid, yellow; stylar region truncate; stigma punctiform. Infructescence with 1 – 5 berries; fruit obclavate to ovoid or ellipsoid, 10 – 17.5 x 10 – 14 mm, deep green ripening to scarlet, epidermis of upper part of ovary roughened in submature fruits, more or less smooth when ripe. Seeds c. 3 – 6 mm diam., ellipsoid to compressed-globose.

Distribution — Indonesia (Sumatera), Peninsular Malaysia, Thailand.

Habitat & Ecology — Rain forest on granitic rock along stream. 50 – 300 m.

Note — A large distinctive climber which, for the area under review, has so far been collected only in Yala and Narathiwat provinces of peninsular Thailand where its occurrence is sporadic. The large yellow-and-white inflorescences are most similar in appearance to those of P. gigantipes. However, the form of the mature and juvenile leaves of these species is quite different (compare Figs 6, 6a with 3, 3a). Sterile P. macrocephalus can be confused with P. scandens although in the latter the petiole is generally shorter than the lamina and overall P. macrocephalus is a more massive plant.

Geographically representative selection of collections studied:
THAILAND. PEN75. Yala: Than Tio, 006° 20’N, 101° 20’E, 25 April 1974, Geesink & Hattink 6437 (fl., fr.) (BKF, K, L). PEN76. Narathiwat: Sungei Kolok, Nikom Waeng, 005° 50’N, 101° 50’E, 1 March 1974, Larsen & Larsen 32765 (fl.) (AAU, BKF, K, L, P).