Recent phylogenetic studies have revealed that four species of Australian Rhamnaceae, tribe Pomaderreae Reissek ex Endl., should be assigned to a new genus. This paper describes Polianthion K.R.Thiele, including one new species, P. collinum Rye, and makes the relevant combinations for P. bilocularis (A.S.George) Kellermann, P. wichurae (Nees ex Reissek) K.R.Thiele and P. minutiflorum (E.M.Ross) K.R.Thiele. The genus is defined by having two carpels, a characteristic dense stellate indumentum on both vegetative and floral parts of the plant, free stipules, long-pedicellate flowers and fruitlets dehiscent for their full length. Three species are found in the south-west of Western Australia and one in eastern Queensland.