Abstract
A new mycoheterotrophic species, Thismiaaliasii, is described and illustrated. This species inhabits a hill dipterocarp forest in mountains of eastern Peninsular Malaysia. Thismiaaliasii differs from other Thismia species by the following features: tepals equal in size and shape with different length of their appendages, appendages of the outer tepals shorter than those of the inner tepals (3.5 mm vs. ca. 26-32 mm long), stamen supraconnective at apex with three long filiform appendages and two acute appendages, and the margins of individual connectives abaxially raised into a conspicuous rib. With respect to floral morphology, T.aliasii should be placed to Thismiasubsect.Odoardoa. According to the categories and criteria of the IUCN Red List, T.aliasii is provisionally classified as Critically Endangered (CR).