Tree 5-30 m. Leaves chartaceous or thinly coriaceous, oblong(-lanceolate), 12-30 by 3.5-10.5 cm, base attenuate to rounded, apex blunt to acute; Inflorescences: Fruits 1-3 per infructescence, ellipsoid, broadly rounded at both ends, early glabrescent (hairs not known), bright brown, 5-6 by 4-4.5 cm;
Knema viridis belongs in the group of K. curtisii, and seems most related to K. linguiformis. It is markedly stouter in all parts, with larger leaves, and stouter male buds with shorter hairs, and larger fruits with spongy dry, very thick pericarp (1 cm). The fruits of the related K linguiformis are 3.5-4 cm long with fruiting pedicel up to 8 mm long and pericarp 1-2 mm thick, but with seeds of about the same size as those in K. viridis (seeds 25-30 mm long). Male buds of K. linguiformis may reach 6 mm diameter, but the flower is more delicate, with woolly hairs up to 0.4 mm long. Knema viridis also shows affinities with K. woodii, with similar twigs and thick perianth lobes, a similar obconical androecium (but with the anthers spaced, not tightly appressed), and a pistil with the ovary narrowed into a slender style-like part.