This report describes Thismia belumensis Siti-Munirah & Suhaimi-Miloko, a novel species of achlorophyllous herb discovered in the Royal Belum State Park, Peninsular Malaysia. This new species is unlike any previously described species of Thismia . In particular, T. belumensis possesses a unique annulus, which has been expanded and modified into a cucullate (hood-like) structure. This structure covers the apical floral tube and has an opening on one side facing a thickened part of the annulus, and the off-centre floral aperture confers a zygomorphic symmetry to the flower, indicating T. belumensis is more similar to Thismia labiata J.J.Sm. This morphological detail makes this new species distinct from all other described species of Thismia . In this report, we provide descriptions, illustrations, colour plates, and the provisional conservation status of Thismia belumensis .