Quaqua mammillaris, sometimes called aroena, is a stem succulent that forms clumps, typically growing to 30 cm in height, occasionally much taller. The erect stems branch from a single, centrally rooted base; branching may also occur higher up along the stems. The stems are four- to seven-angled with stout, pointed tubercles or conical teeth spaced upon bulges of the stem ridges. Stems become up to 4 cm in diameter.
The flowers of 2,5 cm in diameter have long, spreading corolla lobes, narrow and dark maroon or purple in colour. There is purple speckling in the creamy white flower centre.
Q. mammillaris occurs from the Little Karoo across Namaqualand into Namibia (Vlok and Schutte-Vlok, 2010; Le Roux, et al, 2005).