The Tricostularia Nees ex Lehm. group of genera is reviewed and formally recognised as Cyperaceae tribe Schoeneae subtribe Tricostulariinae R.L.Barrett, K.L.Wilson & J.J.Bruhl. Molecular data from plastid rbcL and trnL-F and nuclear ITS and ETS regions are combined with a novel assessment of morphological characters to support our new classification. Six genera are included: A new genus, Ammothryon R.L.Barrett, K.L.Wilson & J.J.Bruhl, and the named genera Chaetospora R.Br., Morelotia Gaudich., Tetraria P.Beauv., Tricostularia, and Xyroschoenus Larridon. Ammothryon, Chaetospora and Tricostularia are all endemic to southern Australia. Morelotia has one species each in Hawaii, French Polynesia and New Zealand, and three species in southwest Western Australia. Tetraria has a disjunct distribution in Southern Africa, Borneo, New Guinea and New Caledonia. Xyroschoenus is endemic to the Seychelles. Tetrariopsis C.B.Clarke (based on Tetrariopsis octandra (Nees) C.B.Clarke) is included under an expanded concept of Morelotia, which also includes Tetraria australiensis C.B.Clarke and Tetraria microcarpa S.T.Blake from south-west Western Australia. Tricostularia bennettiana R.L.Barrett & K.L.Wilson, Tricostularia davisii R.L.Barrett & K.L.Wilson, Tricostularia lepschii R.L.Barrett & K.L.Wilson, Tricostularia newbeyi R.L.Barrett & K.L.Wilson, and Tricostularia sandifordiana R.L.Barrett & K.L.Wilson are described as new species from south-west Western Australia. The following new combinations are made: Ammothryon grandiflorum (Nees ex Lehm.) R.L.Barrett, K.L.Wilson & J.J.Bruhl, Morelotia australiensis (C.B.Clarke) R.L.Barrett & K.L.Wilson, Morelotia microcarpa (S.T.Blake) R.L.Barrett & K.L.Wilson, Morelotia octandra (Nees) R.L.Barrett & J.J.Bruhl and Tricostularia drummondii (Steud.) R.L.Barrett & K.L.Wilson. Tricostularia drummondii is reinstated from synonymy (formerly Discopodium drummondii Steud.), having previously been confused with T. exsul (C.B.Clarke) K.L.Wilson & R.L.Barrett. Lectotypes are selected for Chaetospora flexuosa var. gracilis Boeckeler, Discopodium drummondii Steud., Elynanthus grandiflorus Nees ex Lehm., Lampocarya affinis Brongn., Lepidosperma exsul C.B.Clarke, Morelotia gahniiformis Gaudich. var. minor A.Rich., Tetraria australiensis C.B.Clarke, Tetraria capillacea var. intercedens Kük., Tricostularia compressa Nees ex Lehm. and Tricostularia neesii Lehm.