Three grass smuts are recorded from tropical Australia. Sporisorium simile destroys the inflorescence of its host Chionachne in tropical Western Australia. It is distinct from the inflorescence smut Sporisorium reilianum, here recognised for the first time on Chionachne, in Queensland, and from the ovary smut Ustilago polytocae, found on Chionachne in India. Recent use of binomials based on Ustilago holci-sorghi Rivolta for the smut named S. reilianum is discussed and not recommended. Ustilago brunkii is recorded from leaf sheath lesions on Dichanthium in tropical Western Australia. Comparison with a collection of this species from Texas, U.S.A. and with the type species of Jamesdicksonia from India indicates that U. brunkii is best placed in Jamesdicksonia. The identity of its known grass hosts in the U.S.A., Central America and Australia, and their significance in its taxonomy, are discussed.