Austrothemis is a genus of dragonflies in the family Libellulidae, endemic to southern Australia. The single known species, Austrothemis nigrescens, is commonly known as the swamp flat-tail. It is endemic to southern Australia, where it inhabits lakes and swamps. It is a small dragonfly; the male has a flattened abdomen with black and red markings, and the female has black and yellow markings.

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