Drosera purpurascens is a fan-leaved tuberous sundew in the Stolonifera complex. It is distinguished from its relatives by its compact morphology and long petioles. These petioles emerge out of the basal rosette in smaller plants or are borne on relatively short semi-prostrate stems. The flower scape emerges directly from the basal rosette. The specific epithet refers to the way herbarium specimens develop a purple coloration, although living specimens are commonly a deep crimson.
The species grows in the south west of Western Australia, although it is absent from the west coast plain. It inhabits sandy laterite or clay substrates in heathland and woodland, as well as on some granite outcrops.
Drosera purpurascens is closely related to other members of the Drosera stolonifera complex. It was previously described as D. stolonifera subsp. compact, in reference to its compact morphology. It is distinguished from D. stolonifera by its long petioles, which often emerge directly from the basal rosette, as well as the shorter stems. The species is also very similar to D. monticola, which inhabits the summit regions of peaks in the Stirling Range and shares the long petioles and red coloration (D. purpurascens is found in the lowlands there). D. purpurascens is morphologically separated by its emerging stolon, which runs horizontally when breaking out of the ground.