Austrothemis nigrescens is a species of dragonfly of the family Libellulidae, 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.

Austrothemis nigrescens is the only species in the genus Austrothemis.

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