Poikilospermum is a genus of about 20 species found in India, Indochina and Malesia (Chew 1963). Eight are recorded from Borneo, three of which are endemic. Two subgenera are recognised. Subgenus Ligulistigma has 15 species in West Malesia; it has capitate inflorescences with a branched peduncle. Subgenus Poikilospermum has four species in East Malaysia and one Philippine endemic. Its inflorescences are not capitate. The new species described below, P longifolium, is in subgenus Ligulistigma and is distinguished most obviously from other species by lamina length and width. This feature, with the twice-branched female inflorescence, large female capitula and stipules, form a unique combination in the genus that separates this taxon from the other species of Poikilospermum. Like other species of the subgenus, it has elongate cystoliths on the lamina. There are two types of pubescence. The first consists of long, transparent and unicellular hairs, which are common on the abaxial leaf surface and petiole, and sparse on the adaxial leaf surface. The second is short, multicellular, brown hairs distributed evenly on both leaf surfaces and the petiole. In fresh material the leaves are lime-green above, the inflorescence stalk is pale yellowish-pink and the capitula are purple. Although it is known only from a pistillate individual, Poikilospermum longifolium can readily be inserted into Chew's key (1963), page 61 as follows: