Drosera slackii is a rosetted sundew endemic to the Western Cape in South Africa. The species is named after Adrian Slack, a well-regarded authority on carnivorous plants.

Drosera slackii grows a rosette of semi-raised leaves that usually reach around 5cm in diameter. The leaves are shaped like the body of a guitar, with a petiole that is expanded in the middle and a dilated lamina. The leaves are usually very slightly raised off the ground. The undersides of the unfurling leaves are sparsely covered in short, fleshy projections. The plants are usually bronzed to red in colouration.

The species is endemic to the Western Cape in South Africa, where it grows in the coastal ranges of the Kogelberg, Hottentots-Holland and Kleinrivier Mountains. It inhabits permanent seepages along small creek lines in mountainous areas. The species does

Drosera slackii is superficially similar to many of the rosetted sundews of South Africa, but is distinguished by the guitar-shaped leaves and fleshy leaf projections on the undersides of the unfurling leaves. It is most similar in leaf shape to D. rubrifolia, but the latter species lacks underside leaf projections.