Description from Flora of China
Climbers. Stems obviously ridged and furrowed when dry, glabrous. Petiole 3-3.5 cm, shortest on leaves toward apex of stem, sparsely hispidulous; prophyll 3-7 mm; leaf blade ovate-orbicular or ovate, 8-11 × 5-8 cm, membranous, glandular, abaxially sparsely hispidulous, especially on veins, adaxially glabrous, base rounded to subcordate, usually truncate, rarely shortly tapered on apical leaves, symmetric or slightly oblique, apex cuspidate or mucronate; veins 7(-9), apical pair arising 0-5 mm above base, reaching leaf apex, others basal. Flowers monoecious. Spikes leaf-opposed. Male spikes 8-14 cm, slender; bracts oblong-obovate, apex rounded, ca. 2 × 0.6-1 mm, adnate to rachis, margin free, apex ± rounded. Stamens 2-4; filaments nearly as short as anthers; anthers ovoid. Female spikes 7-9 cm, to 18 cm in fruit; peduncle 5-8 mm; rachis sparsely hairy around ovaries; bracts shallowly cupular, ca. 3 × 1 mm, to 4 mm in fruit, glabrous. Ovary ovoid, distinct; stigmas 4 or 5, linear. Drupe drying black, ovoid to globose, ca. 3.5 mm in diam. Fl. Oct-Dec.
Some recent authors have combined this species with Piper bantamense Blume, from Indonesia (Java). However, that species differs from P. attenuatum as follows: petiols shorter, 1-1.8 cm, sheath more than 2/3 as long as petiole; leaf blade usually elliptic, sometimes ovate, 5-7-veined, apical pair of veins usually arising ca. 1 cm above base, base obtuse or broadly cuneate, apex acute to acuminate; peduncle about as long as or longer than petiole.
Wet places within forests. W Yunnan [Bhutan, India]