Branchlets sparsely puberulent. Leaves opposite; Inflorescence of axillary and/or pseudoterminal cymes, 5.5-13 cm long; Sepals ovate, 1-1.9 by 0.7-1.6 mm, 0.9-1.9 times as long as wide, apex acuminate to obtuse, sparsely puberulent. Stamens inserted at 0.8-1.3 mm from corolla base which is 0.2-0.4 of tube length; Ovary 0.8-1.4 mm long; Fruit linear, glabrous, 9.5-14.2 cm by 8-9 mm. Seeds:
Asia-Tropical: Maluku (Maluku present); New Guinea present, Ceram present, Halmahera present
Malesia: Moluccas (Halmahera, Ceram), New Guinea.
This species is easily distinguished from all others by the large projections on the sides of the filament. Sterile specimens are easily mistaken for the more common P. buruensis although they are not particularly closely related. Distinguishing them can be difficult but P. rubra tends to have thicker, more glaucous leaves.