Small tree 8 m. Leaves chartaceous(-coriaceous), (ovate-)oblong, 15-25 by 5.5-8(-9) cm, base broadly rounded, apex acute-acuminate; Inflorescences:
Asia-Tropical: Philippines (Philippines present), NE Luzon present, Palanan area present
Malesia: Philippines (NE Luzon, Palanan area; known only from the type).
This species is superficially reminiscent of K glomerata (especially in the leaves) and K. tomentella (as regards the conspicuous indumentum, falling off in pieces). Knema ridsdaleana is readily distinguishable by its grey leaf undersurface, with minute dark punctation (not to be confused with coarser dots, strong lens!), conspicuous indumentum, long-stalked (male) inflorescences, 4-merous perianth, with conspicuously shedded indumentum, and 11-13 large (long) ± contiguous subsessile 4-sporangiate anthers.